Welcome!

Hello, I am Andy Zhu, I am a high school student at St. George's School an undergrad at the University of Cambridge interested in Competitive Programming. This repo is just for me to review my own solutions

andy_zhu23 on DMOJ

Wizard_of_Orz on codeforces

Wizard_of_Orz on LeetCode

Wizard_of_Orz on AtCoder

to do list

task	date	time

past events

task	date	time	score	reflection
CCC 2023	Feb 15th	8:00am	63	FINALLY HAD ONE GOOD CCC
USACO Jan 2022 Platinum	Jan 30th	9:00	100	too hard
USACO Dec 2022 Platinum	Dec 19th	9:00	550(90th)	Solved 1 problem, solve 2 next time :)
CF 825	Oct 10th	7:35	3829(131st best so far)	Very good job skipping C2 and did D
CF 824	Oct 2nd	7:35	3593(192nd best so far)	took too long to solve A and B
CF 821	Sept 19th	7:35	3772	bruh actually didn't think of dp for D2
CF 819	Sept 6th	7:35	2980	too slow, clear array for every test case
CF 813	August 13th	7:35	2876	didn't solve D :(
CF 812	August 6th	7:35	2806	didn't solve D :(
CF Edu_133	August 4th	7:35	3	didn't solve C, I am a failure :(
CodeTon 2	July 31st	7:05	3167	Do problems faster
CF 804	July 4th	7:35	2732	Didn't solve D :(
CF 803	June 28th	7:35	1857	got hacked :(
DMOPC	June 27th	9:00	235	failed to solve P2, actually took 2 hour to think, brain is so slow
CF Global 21	Jun 25th	7:35am	5148(first time solve 5 problems!!!)	made such a stupid mistake for E
CF 801	Jun 18th	7:35am	2071	picked the wrong root
CF Edu_130	Jun 12th	7:35am	4/6	Too many wrong subs!!!
CF 796	Jun 3rd	7:35am	2455	Got trolled by C, should've looked at E
CF 795	May 31st	7:35am	3592	should've checked C before submitting
ACSL Final	May 28th	whole day	35(Silver Medal)	problem so cancer
CF Edu 129	May 23rd	7:35am	3	you win some, you lose some
mBit	May 22nd	10am	2/10	should've looked at the leaderboard to do easier problems
CF 793	May 22nd	7:35	4151(211th best so far)	I shouldnt've made 3 wrong sub for C
CF 789	May 8th	7:35	3081(266th best so far)	didn't solve D :(
CF 788	May 6th	7:35	4021	actually failed A cause didn't put equal sign
CF 785	Apr 30th	7:35	2457	really close to solve D
DMOPC Apr	Apr 24th	9:00	210	too slow debugging for P2
CF 782	Apr 17th	7:35	3197(482nd best so far)	too slow, made so many WA on B
MALD 1	Apr 16th	9:00	310	actually failed C Orz
USACO US Open 2022 Platinum	Mar 28th	6:00	0	Orz Orz Orz
USACO US Open 2022 Gold	Mar 27th	1:00	1000	I love Bessie!!!
CF Edu 125	Mar 22nd	7:35am	3 problems	need improvement
Google Kickstart	Mar 19th	9:00pm	58	throw less template, wrong manacher alg
SAC Code Challenge 4	Mar 13th	9:00	500(AK)	too slow debugging
CF 777	Mar 11	6:35	2707	fail to consider some cases for D
USACO 2022 Feb	Feb 25th-28th	9:00	531	get better at expected dp
CF 772	Feb 20th	6:35	4076(best so far 558th)	very good in terms of accuracy, but need improvement on time
CCC Senior	Feb 16th	8:00	43	I shouldn't have focused on S5, I am actually bad
DMOPC 21 Feb	Feb 10th - Feb 14th	9:00	52	P4 use bfs instead of dfs, go from the point not on path
CF 770	Feb 6th	6:35am	2844	look at parity
USACO 2022 Jan	Jan 28th - Jan 31st	9:00	438	so clooooose to plaaaat
An Animal Contest 5	Jan 21th - Jan 24th	9:00	410 (8th best so far)	keep it up, should've looked at P5 more
DMOPC Jan	Jan 13th - Jan 17th	9:00	220	should've done P3, instead of focusing on P5
Mock CCC Senior 2	Jan 2 - Jan 16th	9:00	45	could've done P3, overcomplicated it
Hello 2022	Jan 3rd	6:35am	2140	I should just start from D next time
BSSPC 21 Senior	December 26th - December 29th	9:00	330 (15th place best so far)	think of out of bound earlier when debugging
An Animal Contest 4	December 23rd - December 27th	9:00	340	should've got full for problem 4
DMOPC December	December 17th - December 20th	9:00	205	left the last hour, should've been able to solve P3
CF Deltix Autumn	Nov 28th	6:35 - 8:05	3680	For D, I thought too much, should've just read data size more carefully
CF 756	Nov 25th	6:35 - 8:50	4/8	Got hacked for E1, F considered an extra step that is wrong
DMOPC November	November 12th - 15th	9:00	210	Should've finished first problem quicker
DMOPC October	October 8th -11th	9:00	230	should've attempted interactive, for problem 4 should've known how to do it
CF 747	Oct 8th	7:35 - 9:35	2764	too dumb, too slow
CF 746	Oct 3rd	7:35 - 9:35	1210	very sad that I missed on condition in the if statement for C
CF 742	Sept 5th	7:35 - 9:35	2921(first time solve 2250)	Good thing I solved E
DMOPC September	Sept 4th	9:00 - 9:00	200	I need to learn interactive problems!
CF Deltix21	Aug 29th	7:35 - 10:35	1298	Need more practices!
CF 741	Aug 26th	7:35 - 9:35	1276	Think case by case, and be patient when doing rough works
CF 740(div 2)	Aug 24th	7:35 - 10:05	3678(598th/best so far)	don't get stuck on using segment when you can use prefix sum
Kickstart round E	Aug 21st	8:30 - 11:30	1062th place	this one is hard
CF 739	Aug 18th	7:35am	4/7	Try to check answer before submission next time
CF 738	Aug 15th	7:35am	3254/best so far(798th)	Should do questions faster and made one false submission
CF 737	Aug 9th	7:35am	1330	My brain too slow, do those questions faster
An Animal Contest 3	Aug 3rd	9:00pm	400/800	do questions faster, at least got back to purple
CF Edu_112	July 30th	7:35am	3/6	Getting back some skills after undergone 20 days of hell
CF 728 (Div 2)	Jne 24th	8:35 am	2342	could've completed them faster
CF 727	June 20th	3:05 am	2108	Almost got the fourth question, could've finished problems quicker
DMOPC 21' June	June 18th - June20th	9:00 am	120	For the second question I don't know how to output answers clockwise
CF LATOKEN	June 13	8:35 am	2366	Too dumb to do interactive problem. Also remember to check long long before submission
DMOPC '21 May Contest	May 28 - May 30	9:00 am	300	question 4 USE SET I am so dumbbbbb
An Animal Contest 2	May 7th - May 10th	9:00 pm	230	should've done question 3
DMOPC '21 April Contest	April 23 2021 - April 25 2021, 2021	21:00 PDT - 21:00 PDT	200	Should've gotten partial for question 3
Google Kickstart 2021 round B	April 18th	4:00am	41/100	good thing I got partial for C and D
Codeforces Round #713	April 10th	7:35am	4/7	I ran out of time
USACO 2021 US Open	April 2nd	9:00am	394/1000 (Gold)	P2 and P3 are out of my skill range currently
USACO 2021 Feburary	Feb 17th	9:00am	800/1000 (Silver)	P2 make the array bigger
USACO 2020 December	Dec 18th	9:00am	900/1000 (Bronze)	Final question using discretization

problems

CSP

Source	Problems	status	skills needed	rating
CSPS 2021	T2	complete	dp, using multiple states	***
CSPJ 2022	T4	complete	dp	**
CSPJ 2022	T3	complete	stack	**
CSPJ 2022	T2	complete	binary search	**
CSPJ 2022	T1	complete	don't be dumb	*
CSPS 2022	T3	complete	kind of hashing, simplify the problem	****
CSPS 2022	T1	complete	travel two places, use math to combine cases	***
CSPS 2022	T2	complete	use multiple sparse tables	**

HDU

Source	Problems	status	skills needed	rating
HDU	Winner Prediction	complete	greedily let 1 win for every m2 games containing 1, dinic all other games	***
HDU	Matryoshka Doll	complete	dp	***
HDU	Origrimmar	complete	answer is the same regardless, just simulate	*
HDU	backpack	complete	bitset, dp	***
HDU	ball	complete	bitset, sorting	***
HDU	copy	complete	do operation in reverse, bitset	***
HDU	Link with Level Editor II	complete	two pointer, matrices	***
HDU	Shinobu loves trips	complete	math	**
HDU	Luxury cruise ship	complete	do dp till the LCM of all three numbers	***
HDU	Static Query on Tree	complete	segtree, hld, binary lifting	***
HDU	alice bob	complete	2 Ns can be viewed as 1 N - 1	**
HDU	random	complete	understand expected value	*

mBit

Source	Problems	status	skills needed	rating
2022 Spring	P7	complete	knapsack	**
2022 Spring	P9	complete	get result with first time, check with all other times	***

NOIP && NOI

Source	Problems	status	skills needed	rating
NOI 2009	P4	complete	minimum cut, get rid of cycle with tarjan	***
NOI 2008	P3	complete	max flow, assume hire inf employers and build graph	***
NOI 2006	P4	complete	minimum cut, flow means profit lost	****
NOIP 2015	Substring	complete	dp, rolling array	***
NOIP 2016	toy	complete	easy implementation	**
NOIP 2016	classroom	complete	expected value dp	***
NOIP 2016	earthworm	complete	maintain three values, get max every time	***

Yet Another Contest

Source	Problems	status	skills needed	rating
C2	P6	complete	li chao tree, convex hull trick	****
C2	P4	complete	prim	**

An Animal Contest

Source	Problems	status	skills needed	rating
C7	P5	complete	find diameter	***
C7	P3	complete	binary search or two pointer for the position using and not using portal	**
C7	P2	complete	reorganize the tree	*
C7	P1	complete	case by case	*
C6	P3	complete	math, frequency array	***
C5	P6	complete	centroid decomposition, LCA, dijkstra	*****
C5	P5	complete	fenwick, two pointer	****
C5	P4	complete	binary search, move big number first	***
C5	P3	complete	dfs with range	**
C5	P2	complete	query 1 with all other numbers	*
C5	P1	complete	super easy implementation	*
C4	P4	complete	throw l bananas, throw randomly doesn't matter, but last throw go to f	**
C4	P3	complete	choose a reference coordinate, if two points with the same slope shoot to the same reference, then they form a pair	**
C4	P2	complete	maintain a prefix lcm, and binary search	***
C4	P1	complete	super easy implementation	*
C3	P4	complete	greedy, a bit of math	***
C3	P3	complete	sorting, greedy	**
C3	P2	complete	greedy	*
C3	P1	complete	implementation	*
C2 P1	Koala Konundrum	complete	greedy	**
C2 P2	Koala Party	complete	case enumeration	**
C2 P3	Koala Balloon	complete	binary search, prefix sum	***
C2 P4	Koala Gambling	complete	case enumeration, greedy	***
C2 P5	Koala Carnival	complete	Segment Tree, two pointer, binary search	*****
C2 P6	Koala Transport System	complete	heavy light decomposition	***

Google Kickstart

Source	Problems	status	skills needed	rating
22 Round B	Problem C	complete	interval dp, a dimension to maintain right or left it was transitioned	***
22 Round B	Problem B	complete	brute force	*
22 Round B	Problem A	complete	math	*
22 Round A	Problem C	complete	bitmask dp	***
22 Round A	Problem B	complete	math	*
22 Round A	Problem A	complete	super easy implementation	*
21 Round H	Problem B	complete	fake dp	*
21 Round H	Problem A	complete	Greedy	*
21 Round F	Problem A	complete	binary search	*
21 Round E	Problem C	complete	Disjoint Set Union, merge palindrom elements	***
21 Round E	Problem A	complete	shuffle string by swaping	*
21 Round B	Problem D	complete	Segment Tree, offline/unsynchronized calculation, dfs	****
21 Round B	Problem C	complete	Maximum interval between primes	**
21 Round B	Problem B	complete	Pre-fix Sum, total three cases	**
21 Round B	Problem A	complete	enumeration	*

DMOPC Problems

Source	Problems	status	skills needed	rating
DMOPC 19 c3	P4	complete	dp	**
DMOPC 19 c7	P4	complete	matrix	***
DMOPC 19 c7	P5	complete	cdq divide and conquer	***
DMOPC 16 c4	P4	complete	Mo's algorithm	**
DMOPC 19 c4	P3	complete	dp	**
DMOPC 19 c6	P4	complete	map on fenwick tree, don't use segment	**
DMOPC 15 c5	P5	complete	don't use HLD, use fenwick + Euler tour	**
DMOPC 22 c2	P2	complete	inverse pair	**
DMOPC 22 c2	P3	complete	use graph theory, topological sort	***
DMOPC 18 c3	P4	complete	find centroid of all z, then sum of depth	***
DMOPC 19 c2	P3	complete	20 fenwicks	**
DMOPC 21 c10	P2	complete	either not move 1, not move 2, or move 1 and 2	**
DMOPC 21 c10	P1	complete	basic stack	*
DMOPC 20 c7	P5	complete	literally samething as NOI06p4, just gotta do ll	****
DMOPC 21 Apr	P2	complete	odd even have same sum	**
DMOPC 21 Apr	P1	complete	easy multiset	**
DMOPC 21 Mar	P2	complete	linked list	**
DMOPC 21 Feb	P4	complete	A to B cover up C or D	***
DMOPC 21 Feb	P3	complete	bfs with pq	**
DMOPC 21 Feb	P2	complete	greedy, just consecutive 0s are important	**
DMOPC 21 Feb	P1	complete	greedy	*
DMOPC 21 Jan	P2	complete	game theory dp, only three possible cases	***
DMOPC 21 Jan	P1	complete	odd number first, then even number	**
DMOPC 21 Jan	P1	complete	number theory	*
DMOPC 21 Dec	P3	complete	nothing to do with coding, pure math	**
DMOPC 21 Dec	P2	complete	prime sieving	*
DMOPC 21 Dec	P1	complete	geometry and slopes	*
DMOPC 21 Nov	P4	complete	use DSU to merge groups, use segtree that store sizes for each value	****
DMOPC 21 Nov	P2	complete	only consider separate into two	***
DMOPC 21 Nov	P1	complete	interactive big brain	**
DMOPC 21 Oct	P4	complete	monotone queue dp, calculate l and r in O(n)	***
DMOPC 21 Oct	P3	complete	randomize all the unknown number	***
DMOPC 21 Oct	P2	complete	two arrays, keep track of index and value	**
DMOPC 21 Oct	P1	complete	binary search, prefix sum	***
DMOPC 16 c4	P5	complete	dsu, dfs	***
DMOPC 21 Sept	P3	complete	interactive, merge two disjoint sets and redirect all edges in each query	***
DMOPC 21 Sept	P2	complete	remove as "consecutive" as possible	**
DMOPC 21 Sept	P1	complete	greedy, go by two each time	*
DMOPC 21 June	P4	complete	heavy light decomposition, store how many son nodes are safe	***
DMOPC 21 June	P2	complete	store lines in a set with pair<pii, pii>	***
DMOPC 21 May	P3	complete	dfs, reverse graph, greedy	***
DMOPC 21 May	P2	complete	greedy	***
DMOPC 21 May	P1	complete	kind of two pointer, greedy	**
DMOPC 15 Contest 2	Personal Assistant	complete	knapsack problem, discretization, binarySearch	***
DMOPC 20 Contest 5	Home Row	complete	enumeration	*
DMOPC 20 Contest 5	On the Clock	complete	enumeration, double inacurrate	**
DMOPC 20 Contest 4	Beautiful Grid	complete	Greedy, enumeration	***
DMOPC 20 Contest 4	Roving Roombas	complete	Block Matrix, binarySearch	****

Mock USACO

Source	Problems	status	skills needed	rating
wlxsq	华盛顿的斧子	complete	DSU, kruskal	***
wlxsq	绝地求生	complete	segtree	***
wlxsq	红叶配绿花	complete	binary search, subtract red by a value	****
wlxsq	招待	complete	ternary	**
wlxsq	小说	complete	two dimensional dijkstra	**
wlxsq	DNA	complete	easy hashing	**
wlxsq	种树	complete	dp	***
wlxsq	旅游景点	complete	graph don't have to be connected, lca, connect edges not connected to node 1 ~ k first	**
wlxsq	calc	complete	binary lifting	****
wlxsq	travel	complete	dfs	*

USACO Problems

Source	Problems	status	skills needed	rating
USACO 2022 Dec Platinum	P1	complete	only run dfs if going through edge is better, this solution probably cheese	***
USACO 2022 Dec Platinum	P2	complete	dsu, merge small to big	***
USACO 2021 Jan Platinum	P1	complete	segtree maintain the number of numbers not swappable before the current number	***
USACO 2020 Jan Platinum	P1	complete	dsu, dp on DAG	**
USACO 2019 Dec Platinum	P2	complete	Euler tour, remove operations using bst	***
USACO 2021 Dec Platinum	P1	complete	segment tree store graph, build reverse graph, create super node, make sure every given segment is a single point	****
USACO 2017 Feb Platinum	P2	complete	segment tree to store the dp state with the maximum roads you can have with last road on that position	****
USACO 2019 Dec Platinum	P1	complete	interval dp	****
USACO 2021 US Open Platinum	P1	complete	segment tree to calculate number of sets for all l as r is enumerated	****
USACO 2021 Feb Platinum	No time to cry	complete	answer equal to length minus pairs of same color such that they can be drawn with one bruh stroke	***
USACO 2020 Dec Platinum	Sleeping cows	complete	dp, add dimensions	*****
USACO 2017 Jan Platinum	Promotion Counting	complete	Persistent tree, dfs order	*****
USACO 2017 Feb Platinum	Why did the Cow Cross the Road I	complete	Fenwick, shift both a and b	***
USACO 2016 Feb Platinum	Fenced In	complete	Greedy, MST, open up all row or col at once	*****
USACO 2015 Dec Platinum	Max Flow	complete	Lazy, sparse table lca	***
USACO 2015 Jan Gold	P3	complete	layered graph, tarjan	***
USACO 2022 Dec Gold	P1	complete	dp, sort according to x, set x to 0 after using it as much as possible	***
USACO 2022 Dec Gold	P2	complete	monotonic set, use segtree instead of std::set	***
USACO 2022 Dec Gold	P3	complete	greedy forward, dsu backward	***
USACO 2017 Open Gold	P3	complete	pick interval end earliest, use linked list to check whether or not possible	***
USACO 2017 Jan Gold	Hoof, Paper, Scissors	complete	prefix mx	**
USACO 2006 October Gold	Building the Moat	complete	convex hull	**
USACO 2007 Open Gold	Dining	complete	dinic, make each cow an edge	***
USACO 2022 Open Gold	P3	complete	maintain max l and min r for all subtrees	****
USACO 2022 Open Gold	P2	complete	standard dp, 0 and 1 are special cases	***
USACO 2022 Open Gold	P1	complete	realise two inequalities and use map	****
USACO 2022 Feb Gold	P3	complete	only connect nodes from the same row once	**
USACO 2022 Jan Gold	P2	complete	do operations in reverse	***
USACO 2022 Jan Gold	P1	complete	dynamic programming, prefix sum	***
USACO 2018 Dec Gold	fine dining	complete	dijkstra, spfa, create a super node	***
USACO 2021 Dec Gold	pair up	complete	dp, binary search	****
USACO 2021 Dec Gold	HILO	complete	monotonic stack, enumerate rank, and then store position	****
USACO 2019 Jan Gold	sleepy	complete	shortest length is the total length subtract longest decreasing suffix	***
USACO 2019 Jan Gold	poetry	complete	dp, at last, calculate number of ways for one rhyme class, then multiply all together later	***
USACO 2019 Jan Gold	shortcut	complete	dijkstra, build the tree last, very important, otherwise order is messed up	***
USACO 2019 Feb Gold	barn painting	complete	2d lazy, enumerate 2 column and use prefix sum, two rectangle most have one axis to separate	****
USACO 2019 Feb Gold	dishes	complete	binary searching, simulation	***
USACO 2020 Feb Gold	delegation	complete	dp, only one path can lead up the tree, all rest need to be matched	***
USACO 2020 Dec Gold	P3	complete	two pointers, flip the coordinates for easier implementation	****
USACO 2019 US Open Gold	P3	complete	enumerating how many 1s is passed from left to right and vise versa	***
USACO 2019 US Open Gold	P1	complete	dp, sparse table	**
USACO 2019 US Open Gold	P2	complete	minimum spanning tree, the kth biggest edge, prim O(n^2)	***
USACO 2020 Jan Gold	threesum	complete	interval dp, consider two end points to update, use array instead of unordered_map, delete only the added	***
USACO 2020 Jan Gold	boards	complete	segment tree, remember to sort by y as well, write transition out	***
USACO 2020 Jan Gold	Time is Mooney	complete	dp add dimension, reverse graph, remember to initialize	**
USACO 2021 Feb Gold	Stone Game	complete	game theory, mirror moves, find odd occurrence	****
USACO 2019 Dec Gold	moortal cowmbat	complete	dp, floyd algorithm, prefix sum	***
USACO 2019 Dec Gold	milk_pumping	complete	dijkstra's algorithm, another dimension for flow rate	***
USACO 2021 Jan Gold	telephone	complete	only connect the closest breeds, connecting to further cows will only produce same result	***
USACO 2021 Jan Gold	Uddered But Not Herd	complete	bitmask dp, only 20 char, in dp statement, choose a letter to be the most afterward	****
USACO 2020 Dec Gold	Bovine Genetics	complete	dynamic programming, express the last two segments in dp statement	****
USACO 2015 Feb Gold	Censoring	complete	Hashing	****
USACO 2019 Feb Gold	Cow Land	complete	easy heavy light decomposition	***
USACO 2020 Feb Gold	Exercise	complete	knapsack problem, add to n, sum of LCM	****
USACO 2020 Feb Gold	Help Yourself	complete	lazy, each segment contribute 1 when no other segment cover its beginning	****
USACO 2020 Feb Gold	TimeLine	complete	SPFA, remember to include the property less than m	****
USACO 2020 US Open Gold	Favorite Color	complete	disjoint set union, merge edges	***
USACO 2020 US Open Gold	Hair Cut	complete	fenwick, each time add inverse pair end with j	***
USACO 2007 Nov Gold	Cow Relays	complete	binary rate multiply, floyd algorithm	****
USACO 2003 Fall Gold	Puck Just Me	complete	Tarjan	****
USACO Training	Bessie come Home	complete	dijkstra, reverse graph	**
USACO Training	Riding the Fence	complete	Euler Circuit, Hierholzer's Algorithm	***
USACO 2005 Dec Gold	Layout	complete	Bellman-Ford, -1 for negative ring, -2 for not connected. turn Differential constraint into graphs	****
USACO 2011 Open Gold	Mowing the Lawn	complete	monotone queue dynamic programming	***
USACO 2008 Jan	cow race	complete	floyd algorithm	***
USACO 2021 Open Gold	Portals	complete	Kruskal, turn cycles into vertices	****
USACO 2006 Nov Gold	cowfood	complete	bitmasking, dynamic programming	***
USACO 2016 Feb Gold	Fenced In	complete	MST algorithm, separate into horizontal and vertical lines	****
USACO 2019 Dec Gold	Milk Visits	complete	Sparse Table, offline/unsynchronized calculation	****
USACO 2021 US Open Gold	United Cows of Farmer John	complete	enumerate r, binary search l, revisited with Fenwick tree	**
USACO 2008 Nov Gold	Switching light	complete	Segment Tree, interval update	**
USACO 2017 Jan Gold	Balanced Photo	complete	Segment Tree, discretization	**
USACO 2021 Feb Gold	Modern Art 3	complete	Dynamic Programming	***
USACO 2022 Dec Silver	P3	complete	get an answer from adjacent, check the answer	**
USACO 2022 Dec Silver	P2	complete	game theory, realize formula	***
USACO 2022 Dec Silver	P1	complete	first send up, then send down	***
USACO 2017 Dec Silver	P1	complete	psa	**
USACO 2021 Dec Silver	P3	complete	lazy array	**
USACO 2021 Dec Silver	P2	complete	DSU, find length to 1 and n	**
USACO 2020 Jan Silver	Loan_Repayment	complete	skipping repeated terms	***
USACO 2018 Feb Silver	Snow Boots	complete	implementation	**
USACO 2015 Feb Silver	Censoring	complete	Hashing	****
USACO 2020 Jan Silver	Berry Picking	complete	greedy + enumerate berries in Elsie's buckets	***
USACO 2019 Dec Silver	Milk Visits	complete	Sparse Table	**
USACO 2021 US Open Silver	Do You Know ABCs?	complete	enumeration, brute force	**
USACO 2021 Feb Silver	Comfortable Cows	complete	implementation	*
USACO 2021 Feb Silver	Year of the Cows	complete	Greedy	*
USACO 2021 Feb Silver	Just Green Enough	complete	Monotone Stack	****
USACO 2021 Jan Silver	Dance Mooves	complete	DFS, Graph Theory	**
USACO 2021 Jan Silver	No Time to Paint	complete	Prefix Sum, Suffix Sum	***
USACO 2021 Jan Silver	Spaced Out	complete	enumeration, knowing two lines give the whole grid	***
USACO 2020 Dec Silver	Cowntagion	complete	Graph Theory, Tree	**
USACO 2020 Dec Silver	Rectangular Pasture	complete	2D Prefix - sum, Multiplication Principle	****
USACO 2020 Dec Silver	Stuck in a Rut	complete	Discretization, priority_queue, Topological order	*****
USACO 2020 Feb Silver	P1	complete	binary lifting	**
USACO 2020 US Open Bronze	P2	complete	don't be dumb	*
USACO 2016 US Open Bronze	P1	complete	psa	*
USACO 2020 Dec Bronze	Stuck in a Rut	complete	Discretization, priority_queue	*****

CCO Problems

Source	Problems	status	skills needed	rating
CCO 17	P4	complete	sort pillar from greatest to smallest, bitmask dp	***
CCO 16	P5	complete	linesweep, segtree	***
CCO 15	P6	complete	inclusion principle, 2d stuffs	***
CCO 19	P2	complete	heap, simulation, dsu	***
CCO 08	P3	complete	brute force checking, use dep and sz to optimize	**
CCO 03	P6	complete	tarjan	**
CCO 09	P5	complete	segtree, merge operations	**
CCO 18	P3	complete	dp, case by case	***
CCO 18	P2	complete	cancerous thinking	**
CCO 19	P1	complete	bitmask dp	**
CCO 19	P5	complete	same as USACO Dec 2022	**
CCO 01	P6	complete	easily check "will become", use dinic to check "may"/"will not"	***
CCO 11	P4	complete	multiset, greedy	*
CCO 20	P1	complete	coordinate compression, difference array	**
CCO 17	P5	complete	same as buying everything first, assume every item lower than the want value of current one has been obtained	***
CCO 21	P2	complete	brute force dfs	***
CCO 21	P1	complete	separate into two sets, one appear more than 100 times, and another less than 100 times, swap = inversion pair	***
CCO 14	P5	complete	easy greedy	**
CCO 20	P2	complete	number of swap = number of inversion, from last element, search for maximum spot to place	***
CCO 14	P2	complete	run dijkstra from A and B(reverse graph), calculate offline	**
CCO 18	P4	complete	do two binary searches together	***
CCO 16	P6	complete	splay	****
CCO 05	P4	complete	use bitset, prime seiving	**
CCO 15	P6	complete	5 dimension dp, super cancer	***
CCO 22	P2	complete	first check YES/NO, stack to buy umbrella, difference array	***
CCO 05	P5	complete	dp	**
CCO 22	P1	complete	two pointer/binary search, find cycle	**
CCO 15	P4	complete	topological order	**
Mock CCO 18	P2	complete	greedy, break into x + t, x - t	***
Mock CCO 18	P3	complete	second shortest path	***
CCO 12	P2	complete	second shortest path	***
CCO 98	P1	complete	big number	*
CCO Mock 18	P4	complete	check negative cycle with bellman ford	**
CCO 2010	P2	complete	dp on trees, knapsack	***
CCO Mock 19	P1	complete	reverse merge	***
CCO 2014	P3	complete	dp on trees, knapsack	***
CCO 2014	P1	complete	dp	**
CCO 2010	P6	complete	binary lifting	***
CCO Prep	packing up	complete	convex hull trick, use __int128	****
CCO 2018	P1	complete	LCS	**
CCO 2013	P3	complete	find half of perimeter	****
CCO 2015	P2	complete	Bitmasking	****

CCC Problems

Source	Problems	status	skills needed	rating
CCC 2023	J5	complete	easy dfs, optional hashing	**
CCC 2023	S4	complete	sort edge based on C, remove based on dijkstra	**
CCC 2023	S3	complete	case by case, cancerous	***
CCC 2023	S2	complete	enumerate middle and expand	*
CCC 2023	S1	complete	trivial	*
CCC 2022	S5	complete	cancerous tree dp	***
CCC 2022	S4	complete	psa, cancerous counting	***
CCC 2011	S4	complete	maximum flow	**
CCC 2022	S3	complete	put numbers in increasing order	***
CCC 2022	J5	complete	sorted based on x axis	***
Mock CCC 2022 1	S4	complete	Mo algorithm, reset left point, only expanding, don't use vectors or hashing structure, just array	****
Mock CCC 2022 2	S3	complete	hashing	***
CCC 2002	S4 hard	complete	segment tree, change result from i to the rightmost element greater than one	***
CCC 2020	S5	complete	dp, only last position of a burger matters, if need to randomly choose, the subset is always the same	****
CCC 1996	S5	complete	easy minimum segtree	***
CCC 2003	S5	complete	mst, dfs	***
CCC 2019	S5	complete	divide and conquer, best solution for sub triangle is when it crosses the centroid (2/3) n	*****
CCC 2020 on DMOJ	J4_hard	complete	Rolling Hash	****
CCC 2010	S5	complete	DP on a tree, trade memory for time	***
CCC 2003	S4	complete	if all substrings of length X are distinct, then all substring of X+1 should also be distinct	***
CCC 2009	S4	complete	dijkstra	**
CCC 2011	S4	complete	disjoint set, reading input correctly	***
CCC 2010	S3	complete	binary search	**
CCC 2011	S5	complete	bitwise operation, bfs	**
CCC 2019	S4	complete	Dynamic Programming, Sparse Table, Greedy	*****
CCC 2019	S4v2	complete	segment tree, subtract by infinity, no worry about days	****
CCC 2017	S5	complete	block matrix, block[l] == block[r] not l == r	*****
CCC 2018	S5	complete	Calculate Flights and Portals separately, link all portals/flights except those already connected	*****
CCC 2012	S4	complete	Brute Force, BFS, java is op(passing array into queue), c++ pointer	***
CCC 2021	S5	complete	Greedy, Segment Tree, lazy, lcm, gcd	*****
CCC 2013	S4	complete	turn situation into a graph	*
CCC 2013	S3	compelte	enumeration	*
CCC 2019	J5	complete	run dfs twice	***
CCC 2016	S5	complete	Binary rate multiply, xor	*****
CCC 2015	S5	complete	Dynamic Programming, Greedy, four dimensional dp state	****
CCC 2017	S4	complete	Kruskal algorithm, MST problem, run MST twice to see if a non-active pipe can be replaced	****
CCC 2014	S4	complete	Discretization	***
CCC 2014	S5	complete	Dynamic Programming, save the result last time to avoid collision with other results	****
CCC 2020	S4	complete	enumeration, greedy	****
CCC 2020	S3	complete	Rolling Hash, compute hash value twice	****
CCC 2018	S4	complete	Dynamic Programming, multiplication	***
CCC 2021	S1	complete	implementation, double is not accurate	*
CCC 2021	S2	complete	using two arrays instead of a 2d array	*
CCC 2021	S3	complete	Prefix Sum, Binary Search, Math	****
CCC 2021	S4	complete	Reversed graph, Dijkstra, priority_queue	***
CCC 2015	S4	complete	SPFA, add a dimension	**
CCC 2002	S4	complete	Doing dp in an interval	***
CCC 2001	S3	complete	Disjoint Set	**
CCC 2009	S3	complete	toxic	*
CCC 2005	S5	complete	fenwick	**
CCC 2008	S5	complete	game theory dp	**

IOI Problems

Source	Problems	Status	Skills needed	rating
IOI 2015	P4	complete	use log value to compare	**
IOI 2002	P4	complete	convex hull trick	***
IOI 2006	P2	complete	use fenwick on rmq	***
IOI 1998	P4	complete	coordinate compression, line sweep, difference array	**
IOI 2010	P3	complete	binary search, prefix sum	***
IOI 2004	Empodia	complete	montonic stack to store min and max, two nodes is okay if value - index is the same	***
IOI 1996	Network of Schools	complete	Tarjan scc	***
IOI 1994	The Triangle	complete	standard dp	*

Codeforces Problems

Source	Problems	status	skills needed	rating
CF 604	E	complete	minimize $\frac{x^2}{2}$ using max flow	****
CF 884	D	complete	dp, get all factors	**
CF 884	C	complete	dp, odd length can be 0	**
CF 292	D	complete	dsu on tree, diameter of tree	***
CF Beta 3	D	complete	put all ), if not okay, replace with cheapest (	**
CF 722	D	complete	add edges between adjacent nodes	****
CF 872	D2	complete	count number of occurence of edges, + 1 to get result for nodes	***
CF 873	E	complete	manacher + segtree + dp	***
CF 200	D	complete	heavy light decomp	**
CF Edu_111	E	complete	binary search, bitmask dp	***
CF 852	F	complete	binary search for left, everytime decrease by average, use segment tree maintain answer for l	****
CF 845	E	complete	binary search, scc, dsu	***
CF 845	D	complete	expected value	***
CF 845	C	complete	sort, two pointer	**
CF 845	B	complete	math, all permutation are the same	*
CF 845	A	complete	trivial	*
CF Hello 2023	F	complete	odd tree makes no difference even can be turned to 0	***
CF Hello 2023	D	complete	monotonic stack, dsu	**
CF Hello 2023	C	complete	use min or max instead of current element	**
CF Hello 2023	B	complete	do some algebra	*
CF Hello 2023	A	complete	trivial	*
CF Polynomial Round 2022	E	complete	binary lifting	**
CF Polynomial Round 2022	D	complete	two pointer	**
CF Polynomial Round 2022	C	complete	observation	**
CF Polynomial Round 2022	B	complete	sort	**
CF Polynomial Round 2022	A	complete	change everytime see 1	*
CF 832	D	complete	case by case	***
CF 832	C	complete	whoever have the minimum	**
CF 832	B	complete	don't be dumb	*
CF 832	A	complete	don't be dumb	*
CF 831	E	complete	simple dp	**
CF 831	D	complete	only 2 blank spaces are required	**
CF 831	C	complete	let a number be in 2, one of the other number must be either max or min	**
CF 831	B	complete	long long	*
CF 831	A	complete	don't be dumb	*
CF 830	C	complete	realize f(l, r) <= f(l, r + 1), enumerate first 32 non-zero L because of pigeon hole, binary search r	***
CF 830	B	complete	be careful of 0	*
CF 830	A	complete	answer can only be 0, 1, 2	*
CF 829	E	complete	basic expected value	**
CF 829	D	complete	simple math	*
CF 829	C	complete	group with previous one to change sign	**
CF 829	B	complete	greedy	*
CF 829	A	complete	don't be dumb	*
CF Edu_138	E	complete	turn into graph, dijkstra	***
CF Edu_138	D	complete	make sure to either mod or use __int128	**
CF Edu_138	C	complete	binary search	*
CF Edu_138	B	complete	don't be dumb	*
CF Edu_138	A	complete	don't be dumb	*
CF 828	F	complete	go to the next smallest number, do some math for median	***
CF 825	D	complete	group every consecutive two numbers, connect if 01 or 10	***
CF 825	C1	complete	segment tree + binary search	**
CF 825	B	complete	take lcm and check if it is okay	*
CF 825	A	complete	don't be dumb	*
CF 824	D	complete	enumerating, use set	**
CF 824	C	complete	dsu, implementation	**
CF 824	B	complete	math	*
CF 824	A	complete	math	*
CF Global 22	D	complete	topological order	***
CF Global 22	C	complete	logic	**
CF Global 22	B	complete	implementation	*
CF Global 22	A	complete	implementation	*
CF 821	D1	complete	if not two consecutive, then always just use all y	**
CF 821	C	complete	set a[1] = a[n], then update accordingly	**
CF 821	B	complete	always a win follow by some lose	*
CF 821	A	complete	don't be dumb	*
CF Edu_135	D	complete	dp	**
CF Edu_135	C	complete	look at maximum	**
CF Edu_135	B	complete	pattern	*
CF Edu_135	A	complete	easy	*
CF 819	D	complete	dsu, use red to do a tree, remaining edge might form cycle, in that case, relink edges	***
CF 819	C	complete	logic	**
CF 819	B	complete	case by case	*
CF 819	A	complete	case by case	*
CF Edu_134	D	complete	bit by bit, every number in a, there must be a reverse in b	***
CF Edu_134	C	complete	for min, use two pointer, for max, find leftmost r such a[r] > b[r - 1]	***
CF Edu_134	B	complete	check border	*
CF Edu_134	A	complete	don't be dumb	*
CF 813	C	complete	greedy	**
CF 813	B	complete	swap adjacent	*
CF 813	A	complete	easy	*
CF 812	D	complete	interactive, eliminate 3 elements with 2 moves	***
CF 812	C	complete	dp	**
CF 812	B	complete	minimum must be on either side	*
CF 812	A	complete	don't be stupid	*
CF Edu_133	D	complete	dp, cannot make more than around sqrt(N) jumps	***
CF Edu_133	B	complete	don't be stupid	*
CF Edu_133	A	complete	don't be stupid	*
CF 811	G	complete	simple binary lifting	**
CF 811	E	complete	turn everything into 2 suffix and check modulo 20	**
CF 811	D	complete	dp	**
CF 811	C	complete	pattern	*
CF 811	B	complete	don't be dumb	*
CF 811	A	complete	don't be dumb	*
CodeTon 2	E	complete	simulate N times to remove middle 0s, topological sort add up all a	***
CodeTon 2	D	complete	subtracting two sequences	***
CodeTon 2	C	complete	simple math	**
CodeTon 2	B	complete	set up range	**
CodeTon 2	A	complete	check suffix	*
CF 810	C	complete	just at least two columns for every color	**
CF 810	B	complete	basic thinking	*
CF 810	A	complete	big brain observation	*
CF 809	E	complete	LCA, segtree, dsu	****
CF 809	D1	complete	get all numbers, go from small to big	**
CF 809	C	complete	odd even property	*
CF 809	B	complete	odd even property	**
CF 809	A	complete	very easy implementation	*
CF 808	D	complete	just simulate	***
CF 808	C	complete	compute backwards	***
CF 808	B	complete	number don't have to be distinct, ith gcd be i	**
CF 808	A	complete	gcd	**
CF 807	E	complete	turn into binary number add and sub 1s	***
CF 807	D	complete	remove duplicates to check, then store starting and ending position and subtract	***
CF 807	C	complete	record copying position, transition to the original string	***
CF 807	B	complete	always use the most front	*
CF 807	A	complete	easy sorting	*
CF Edu_131	D	complete	turn into intervals, sort based on right hand side	***
CF Edu_131	C	complete	binary search	**
CF Edu_131	B	complete	greedy	*
CF Edu_131	A	complete	easy	*
CF 804	C	complete	maintain l, r, two cases inside outside interval	**
CF 804	B	complete	repeat a pattern	**
CF 804	A	complete	if odd not possible, else two 0s and n/2	*
CF 803	D	complete	cut into two segments and delete swaps outside of current segment	**
CF 803	B	complete	add will only make it worse unless k = 1	**
CF 803	A	complete	xor properties	*
CF Global 21	E	complete	realize pattern is same as number of paths in a matrix, Fermat's little theorem	***
CF Global 21	D	complete	monotonic stack	***
CF Global 21	C	complete	divide all element by m as many times as possible and check whether simplified versions are equal	**
CF Global 21	B	complete	answer is 0, 1 or 2, remove 0s on the side check whether center have 0	*
CF Global 21	A	complete	or all value in a with z	*
CF 802	D	complete	dp, find how long it first i pipes to fill first i first	***
CF 802	C	complete	difference array, greedy	**
CF 802	B	complete	math	*
CF 802	A	complete	math	*
CF 801	D	complete	gotta pick any root degree >= 3, and no need query root	***
CF 801	C	complete	yes if 0 between minimum and maximum	**
CF 801	B	complete	game theory	**
CF 801	A	complete	easy brute force	*
CF 800	E	complete	dijkstra	***
CF 800	D	complete	simple tree dp	***
CF 800	C	complete	some logics	**
CF 800	B	complete	no consecutive 0 or 1 in the end	*
CF 800	A	complete	alternate 1 and 0	*
CF 799	H	complete	maintain minimum prefix sum	**
CF 786	G	complete	find longest path after deleting edges must be deleted	***
CF Edu_127	E	complete	dp on tree, find lexicongraphically smallest possible string and compare	***
CF 130	D	complete	binary search for first position repeated, if no repeat, query 1	***
CF 130	C	complete	delete b first, check all relative position of a and c	**
CF 130	B	complete	prefix sum	*
CF 130	A	complete	don't be dumb	*
CF Edu_86	D	complete	binary search, sorting	**
CF Edu_82	D	complete	bitmask, greedily combine small bags	**
CF 798	D	complete	not lots of useful squares, answer to right minus one, left add one	**
CF 798	B	complete	swaping only adjacent	*
CF 798	A	complete	sort and choose min	*
CF Edu_67	E	complete	dp change root	***
CF 797	G	complete	segment tree, interval merging	**
CF 797	F	complete	simple cycle finding, lcm	**
CF 797	E	complete	mod, two pointer	**
CF 797	D	complete	prefix sum	*
CF 797	C	complete	don't be dumb	*
CF 797	B	complete	don't be dumb	*
CF 797	A	complete	don't be dumb	*
CF 776	E	complete	disgusting implementation	**
CF 672	C	complete	always optimal to choose local min and max	***
CF 558	C	complete	when simplifying lines, consider horizontal and vertical lines	**
CF 550	E	complete	big number addition, division	**
Grakn Forces	D	complete	suffix maximum, get minimum y based on x	***
CF 796	E	complete	get l for all path, sort l, if l is added to answer, keep path, otherwise leave it	***
CF 796	D	complete	initial has nothing to do with added	**
CF 796	C	complete	check parity	**
CF 796	B	complete	easy parity	*
CF 796	A	complete	easy bitmask	*
CF 795	E	complete	dsu merge blue with blue, red with red, remove blue red cross over	***
CF 795	D	complete	monotonic stack, prefix sum, segtree	***
CF 795	C	complete	decrease by either 1 or 10, make sure check causes with one 1, or no 1	**
CF 795	B	complete	no single element	*
CF 795	A	complete	odd even	*
CF 713	C	complete	slope trick, minus i to compute non strictly increasing	***
CF 13	C	complete	slope trick	***
CF Edu_129	F	complete	dfs order, interval update, for all colors get size of separate components	***
CF Edu_129	C	complete	sort two first, do swap sort to generate swap	**
CF Edu_129	B	complete	just +b and mod	*
CF Edu_129	A	complete	don't be stupid	*
CF 260	A	complete	dp	**
CF 793	D	complete	find a root so that next one is 1, connect with previous or root	***
CF 793	C	complete	largest number with only one occurance can be made into two occurances	***
CF 793	B	complete	find all not equal position, & all of them	**
CF 793	A	complete	check same character in the middle	*
CF Edu_128	E	complete	dp	***
CF 792	E	complete	greedy	***
CF 792	D	complete	the k(k-1)/2 is the same for all cases and don't matter when comparing	***
CF 791	C	complete	fenwick, rook not bishop I am terrible at chess	*
CF 791	D	complete	binary search, tarjan find cycle	***
CF 789	E	complete	alternate for cycles	***
CF 789	D	complete	build row answer on the mth last row	***
CF 789	C	complete	prefix sum	**
CF 789	B2	complete	greedy	**
CF 789	B1	complete	implementation	*
CF 789	A	complete	implementation	*
CF 788	D	complete	precompute, answer add by 2 each time a new line cross an old line	***
CF 788	C	complete	do cycle with dsu, remove cycle that are locked by d	***
CF 788	B	complete	largest interval without special characters	**
CF 788	A	complete	move all negative to the front	*
CF 787	F	complete	find path from x to y, brute force subtrees	**
CF 787	E	complete	dsu the letters	*
CF 786	F	complete	maintain last point	**
CF 785	D	complete	check 0, -1, as long as ends don't touch, and lcm(d, q) == r	***
CF 785	C	complete	easy knapsack	*
CF 785	B	complete	find last occurance of the letter, see if any letter not in the interval	**
CF 785	A	complete	type faster	*
CF 783	D	complete	max fenwick, dp, only good making positive segment long, other segment can stay as size 1	***
CF 783	C	complete	enumerate 0 position, brute force	**
CF 783	B	complete	sorting, implementation	*
CF 783	A	complete	easy math	*
CF 782	E	complete	dsu, if answer 0 -> common bit, if answer 1 -> common bit other than 1 before even edge, else answer 2, super node	***
CF 782	D	complete	calculate number of 1s, fenwick	***
CF 782	C	complete	math, prefix sum, greedy	**
CF 782	B	complete	if odd, make a move to first 1, otherwise turn first 2 0s to 1s	**
CF 782	A	complete	just brute force, don't try to be smart	*
CF Edu_126	D	complete	fenwick store difference, increase by the largest first	***
CF Edu_126	C	complete	binary search	***
CF Edu_126	B	complete	precompute answers	**
CF Edu_126	A	complete	put all small number to one	*
CF 780	F2	complete	pigeonhole ignore adjacent, fenwick tree	***
CF 780	F1	complete	easy enumeration	**
CF 780	D	complete	each separate by 0, delete left and right most negative is count is odd	*
CF Edu_125	D	complete	dp, combine D and H	***
CF Edu_125	C	complete	regular can only be length 2, rest are all palindrome	**
CF Edu_125	B	complete	implementation	*
CF Edu_125	A	complete	"Cause first move x second move y"(Leo Liu)	*
CF 777	E	complete	binary lifting, greedy	****
CF 777	D	complete	multiple cases	***
CF 777	C	complete	greedy	**
CF 777	B	complete	check for whole rectangle	**
CF 777	A	complete	only 2 1 are possible	*
CF 772	F	complete	big brain proof, fenwick tree, sort according to r	****
CF 772	E	complete	topological sort, dfs	****
CF 772	D	complete	dp, bitmask	***
CF 772	C	complete	greedy	**
CF 772	B	complete	greedy	**
CF 772	A	complete	bitmask	**
CF 771	D	complete	bfs	***
CF 771	C	complete	dsu, greedy, heap	**
CF 771	B	complete	sort parody	*
CF 771	A	complete	greedy	*
CF 770	D	complete	interactive	**
CF 700	C	complete	greedy	**
CF 770	B	complete	since guaranteed possible, focus on parity	***
CF 770	A	complete	check if palindrome	*
CF 769	D	complete	segtree, binary search	***
CF 764	G	complete	bitmask, go from high bit, dsu, mst	***
CF 764	F	complete	interactive	***
CF 764	E	complete	dp	**
Hello 2022	C	complete	interactive, dfs	**
Hello 2022	B	complete	greedy, farthest segment	*
Hello 2022	A	complete	greedy	*
CF Deltix Autumn21	E	complete	obtain states, and costs to go to other states, maintain states with segtree	****
CF Deltix Autumn21	D	complete	brute force to store the state before arranging any non necessary moves	**
CF Deltix Autumn21	C	complete	dsu, merge consecutive 1s	*
CF Deltix Autumn21	B	complete	just count how many abc are there	*
CF Deltix Autumn21	A	complete	very simple greedy	*
CF 756	F	complete	two pointer	***
CF 756	E2	complete	dp, think of how one branch can protect the other	***
CF 756	E1	complete	use BFS not DFS	**
CF 756	D	complete	basic tree dp	**
CF 756	C	complete	big scam, biggest value forces you to always choose other side	***
CF 756	B	complete	get better at math	*
CF 756	A	complete	answer can only be -1, 1, 2	*
CF 105	D	complete	probability dp	***
CF 399	D	complete	probability dp	***
CF 752	C	complete	check the prefix	**
CF 752	B	complete	greedy, separate all into n, or n - 1 subsets	*
CF 752	A	complete	implementation	*
CF Edu_44	F	complete	hash all character	***
CF Edu_2	E	complete	save the result of heavy node, brute force light nodes	****
CF Edu_65	F	complete	when merging l and r, it is l[i] * (n - i + 1) + r[i] * i	****
CF 748	G	complete	segment tree interval merging, when fully cancel, the only remainings options are alternating brackets	****
CF 748	E	complete	bfs, priority queue, use multiset to lower time complexity	***
CF 748	D1	complete	get difference, and get gcd	***
CF 748	C	complete	binary search	**
CF 748	B	complete	only consider two digits	*
CF 748	A	complete	implmentation	*
CF Edu 115	E	complete	dp[i][j][0/1] means ith row, jth column, coming from above or left	***
CF Edu 115	D	complete	find the number of cases that don't work, subtract from total	****
CF Edu 115	C	complete	um TLEed, should use map	***
CF Edu 115	B	complete	simple implementation	**
CF Edu 115	A	complete	simple observation	*
CF 747	E1	complete	combinatorics	*
CF 747	D	complete	dsu, mark all subsets, get the sum of the maximum possible subsets	***
CF 747	C	complete	mark all factors, answer can only be 0 1 or 2	***
CF 747	B	complete	bitmask, fast_pow	**
CF 747	A	complete	two numbers always work are n and -(n - 1)	*
CF 746	D	complete	binary search, answer is maximum edge, euler tour	***
CF 746	C	complete	Separate into case odd and even, only really need 1 or 2 edges deleted	***
CF 746	B	complete	if one is not at the prooper position and it is stuck, answer is NO	**
CF 746	A	complete	don't use loop, just use math	*
CF global 15	F	complete	all portals after current must be on, fenwick tree	***
CF 744	G	complete	use relative position to the l endpoint to avoid negative index	****
CF 744	F	complete	dfs on zeros, build graph	***
CF 744	E2	complete	fenwick tree or balanced data structure, greedy	***
CF 744	E1	complete	simulate	*
CF 744	D	complete	do meeting one by one greedy, don't just subtract	**
CF 744	C	complete	brute force	*
CF 744	B	complete	reverse when sorting	*
CF 744	A	complete	count A, B, C	*
CF Edu 114	D	complete	priority queue to search max, hash banned, make sure add vis	****
CF Edu 114	C	complete	binary search for hero to send	***
CF Edu 114	B	complete	annoying math	**
CF Edu 114	A	complete	dfs	*
CF 743(div 2)	C	complete	cycle detection, see if it is DAG, then do dp	****
CF 743(div 2)	B	complete	make A or B monotone, then Binary Search	**
CF 743(div 2)	A	complete	move all numbers to the right and then subtract, greedy	*
Global 16	E	complete	separate all component, merge them, order don't matter, no global variable	****
Global 16	D	complete	greedy, fenwick	***
Global 16	C	complete	greedy	**
Global 16	B	complete	greedy	*
Global 16	A	complete	greedy	*
CF Edu_113	D	complete	only both on x or y, binary search, enumerate people add to time not multiply	***
CF Edu_113	C	complete	case by case, for all permutations, k out of k + 1 of them work	****
CF 742	E	complete	interval merging segment tree	****
CF 742	D	complete	greedy, go from highest digit to the lowest digit	****
CF 742	C	complete	big brain observation	****
CF 742	B	complete	working with xor, xor properties	**
CF 742	A	complete	switching U with D and vice versa	*
CF Deltix21	E	complete	turn it into bracket pairing, sparse table	****
CF Deltix21	D	complete	interactive, get numbers three a time, (a & b) + (a ｜ b) == a + b	****
CF Deltix21	C	complete	implementation, details very important	***
CF Deltix21	B	complete	odd even, moving numbers	***
CF Deltix21	A	complete	straight forward	*
CF 741	E	complete	dp, longest prefix substring, only if the first different character is different	*****
CF 741	D2	complete	map, binary search for position, prefix sum	****
CF 741	D1	complete	separate into odd even, prefix sum	****
CF 741	C	complete	case by case	****
CF 741	B	complete	case by case	***
CF 741	A	complete	pick r / 2 + 1, or l	**
CF 740(div 2)	D2	complete	suffix-sum, dp, two cases	****
CF 740(div 2)	D1	complete	any range data structure, dp, two cases	****
CF 740(div 2)	C	complete	turn each cave into a node, sorting	***
CF 740(div 2)	B	complete	brute force, math	**
CF 740(div 2)	A	complete	implementation	**
CF 739	F2	complete	greedy, enumerate digits, using multiset and pointers to make it easier	****
CF 739	F1	complete	precomplete, binary search	***
CF 739	E	complete	first get second answer, then compute first, then check	***
CF 739	D	complete	bit by bit	**
CF 739	C	complete	math, logics	*
CF 739	B	complete	math	*
CF 739	A	complete	implementation	*
CF 738	D2	complete	DSU, try random nodes from random components from the two forests until we have enough edges	*****
CF 738	D1	complete	disjoint set union on two forests	**
CF 738	C	complete	just try to insert the n + 1 node into any interval	*
CF 738	B	complete	greedy, just ulternate B and R	*
CF 738	A	complete	minimum of all is to &(and) all numbers	*
CF 737	C	complete	Fermat's Little Theorem, fast_pow, careful of integer overflow, case by case, working with bit	****
CF 737	B	complete	greedy, sorting, binary search	***
CF 737	A	complete	greedy, setprecision	**
CF 736	C	complete	greedy	***
CF 734	E	complete	big brain dp	****
CF 734	C	complete	sorting	**
CF Edu_112	E	complete	Segment Tree using minimum to check segments, two pointer	****
CF Edu_112	D	complete	Prefix Sum & enumeration	**
CF Edu_112	C	complete	Prefix Sum & greedy	**
CF Edu_112	B	complete	too dumb, consider cases and enumeration	**
CF Edu_112	A	complete	Greedy	**
CF 732 Div 2	C	complete	separate position to even and odd	***
CF 732 Div 2	B	complete	store the postion for each letter	**
CF 728 Div 2	C	complete	greedy, sorting, implementation	***
CF 728 Div 2	B	complete	greedy, enumeration	**
CF 728 Div 2	A	complete	greedy	*
CF 727	D	complete	greedy, kind of discretization	***
CF 727	C	complete	greedy, binary search	***
CF 727	B	complete	prefix sum with alphabet	**
CF 727	A	complete	implementation	**
CF Edu_110	C	complete	two pointer	****
CF Edu_110	B	complete	sort into first even, then odd	***
CF LATOKEN	F2	complete	Tarjan, Greedy(Gassing Bonny), dp on DAG	*****
CF LATOKEN	F1	complete	Tarjan, find all with in degree 0	****
CF LATOKEN	D	complete	bipartite characteristics of trees	***
CF LATOKEN	C	complete	Realize cycle find numbers of cycle	**
CF LATOKEN	B	complete	decrease only when one single column is tall	**
CF 725	G	complete	Binary Search, inequalities	****
CF 725	F	complete	number theory, each digit changed r - l times	**
CF 725	E	complete	implementation, STL	***
CF 725	D	complete	number theory, calculate prime numbers beforehand	***
CF 725	C	complete	binary Search	**
CF 724	D	complete	binary Search, Set
CF 724	C	complete	dynamic programming, pattern	***
CF 724	B	complete	enumerating string properly	**
CF 724	A	complete	analyze the problem to find out pattern on the sample test case	*
CF 520	Company	incomplete	LCA, segment tree/sparse tree	*****
CF 713	Education	complete	enumeration, not greedy	***
CF 713	Permutation by Sum	complete	Greedy, enumerate one by one	***
CF 713	Short Task	complete	Calculate beforehand, number theory	***
CF 708	K LCM	complete	greedy, let all other numbers be 1 only consider the last three	***
CF 702	Old Floppy Drive	complete	Prefix Sum, binarySearch, replace with Maximum	****
CF 702	Advertising Agency	complete	Math, Fermat's little theorem	**
CF 697	Accidental Victory	complete	Binary Search, sorting	***
CF 697	Cleaning the Phone	complete	Sorting, Binary Search	***

SAC Code Challenge

Source	Problems	status	skills needed	rating
c4	J4	complete	binary lifting	**
c4	P5	complete	do all q2, then binary search q1, and then sort	***
c4	P4	complete	sparse table, binary search	**
c4	P3	complete	ternary search	*
c4	P2	complete	dfs	*
c4	P1	complete	implementation	*
c3	P5	complete	string hashing	**
c3	P4	complete	do in reverse order, dsu, lca	***
c3	P3	complete	customized sorting	**
c3	P2	complete	binary search	**
c3	P1	complete	don't be stupid	*

LeetCode

Source	Problems	status	skills needed	rating
Hard	Median of Two Sorted Arrays	complete	priority queue one small one big	**

Other Problems

Source	Problems	status	skills needed	rating
braziloi 19	P2	complete	graph theory	***
JOI 17	P4	complete	dijkstra	***
COCI 07 c6	P5	complete	array of sets, cheesed with clearing map	**
DMOJ	wac1p4	complete	tree dp	***
DMOJ	cpc21c1p6	complete	sort A, do segtree on B and C	***
COCI 22 c4	P2	complete	dp	***
Japan OI	joi13op3	complete	binary search, dynamic programming, 2 pointer	**
Baltic OI	btoi05p5	complete	dp, priority queue	***
COCI 22 c4	P5	complete	segtree	**
Baltic OI	btoi18p6	complete	math, case by case	**
CEOI 17	ceoi17p4	complete	li chao tree, convex hull trick	***
Baltic OI	btoi17p2	complete	matrices segtree	***
DMOJ	wc99sp6	complete	priority_queue	***
APIO 12	P1	complete	dsu on tree	***
COCI 07 c3	P6	complete	array in segtree	**
DMOJ	cheapsegments	complete	sort l, put r into segtree	**
COCI 19 c6	P5	complete	hash, don't dare using aho korasick	***
COCI 07 c1	P5	complete	count big and small	*
SHOI 2012	回家的路	complete	layered graph	**
POI	TEL-Teleportation	complete	layered graph	***
NA	孤岛营救问题	complete	layered graph for all possible key combinations	***
JLOI2011	飞行路线	complete	layered graph	**
Atcoder DP	T	cmoplete	psa	***
DMOJ	invperm	complete	swap first with last, do a cyclic shift	**
DMOJ	Traffic Light	complete	shortest path	**
COCI 22 c1	P5	complete	enumerate r, find l, only logMax possible l	***
COCI 13 c5	P3	complete	hash, stack	*
CEOI 18	P2	complete	find LIS from front and back, try to combine them	**
COCI 16 c7	P4	complete	maintain ending 0s	**
DMOJ	wac3p5	complete	dp, psa	**
DMOJ	acmtryouts1e	complete	dp, psa	**
DMOJ	acc3p4	complete	two segtree, interval update i * a[i] value	***
COCI 17	P4	complete	divid by 2 to brute force, use pbds	***
DMOJ	lemontree	complete	centroid decomposition, minus M at the beginning	***
JOI 22 Final	P2	complete	bs answer	**
DMPG 19	G5	complete	centroid decomposition, LCA, lazy	***
CEOI 09	Harbingers	complete	dp, convex hull trick, ternary search, maintain previous stack	****
Atcoder DP	S	complete	digit dp	**
Atcoder DP	R	complete	matrices	**
Atcoder DP	Q	complete	segtree	**
Atcoder DP	M	complete	prefix sum, dp	**
DMOJ	revdig	complete	easy application of max flow	**
utso15	utso15p5	complete	kruskal, LCA	**
DMOJ	seed5	complete	minimum cut	***
DMOJ	bts18p6	complete	math, difference array	***
DMOJ	Monkey Motel	complete	segtree, dfs order	***
Atcoder	coins	complete	probability dp	**
DMOJ	btoi09p2	complete	same as victor rain	***
DMOJ	higgs	complete	easy segtree	*
DMOJ	A plus B hard	complete	high precision	**
SAC 22 c5	P4	complete	merge interval with two pointer	**
DMOJ	Lexicographically Least Substring	complete	skip already matched, brute force check last position	**
CTU Open 2018	Escalator	complete	bit by bit, dsu	**
apio 2007	Mobiles	complete	tree dp, read problem carefully	**
wlxsq	合并果树	complete	sort using frequency array, coordinate compression	***
Facebook Hacker Cup '15 Round 1	Homework	complete	seive and add 1 to cnt every time seiving	**
第k小值	complete	bs, two pointer	***
DMOJ	Tenri	complete	bitmask dp	**
wlxsq	相遇	complete	LCA	***
wlxsq	包裹传递	complete	bs, same three decimal places	**
DMOJ	Lemon Game	complete	game theory, euclidean alg	**
DMOJ	comparing arrays	complete	hash on segtree	**
DMOJ	hydration	complete	bs for answer	**
DMOJ	Chirstmas Cards	complete	knapsack	**
TJOI	猜数字	complete	chinese remainder theorem, fast multiply	***
DMOJ	N-Kat	complete	the minimum two sets where not completely contained which have best answer is the answer	***
DMOJ	balancing act	complete	easy dfs	*
atcoder	deque	complete	game theory dp	*
dmoj	Levves Loves Segment Tree	complete	dynamic segment tree	**
dmoj	2 Primes	complete	prime sieving	***
dmoj	Dog Girls	complete	kmp, string hashing	***
HDU	Gorgeous Sequence	complete	segment tree, update to min	***
COCI 14c5	P4	complete	implementation	**
dmoj	String Finding	complete	string hashing	*
wlxsq	士兵占领	complete	dinic	***
JSOI	blue mary	complete	li chao tree	***
NOI Online	丹钓战	complete	fenwick tree, monotonic stack	***
wlxsq	运输问题	complete	max flow minimum cost, dinic, EK	**
wlxsq	分配问题	complete	max flow minimum cost, dinic, EK	**
wlxsq	方格取数	complete	max flow, bipartite graph	***
TLE 16 c8	P5	complete	max flow/bipartite	***
ICPC	knapsack 4	complete	dp store difference, random shuffle	***
DMOJ	Kth-Rank Student	complete	pbds ordered set, merge light into heavy	***
wlxsq	可达性统计	complete	bitset	***
DMOJ	Fox Girls	complete	every connected component is tree plus an edge, run tree dp	****
DMOJ	Boxling	complete	fenwick, linesweep	***
DMOJ	Farming Simulator	complete	dp	***
wlxsq	星球大战	complete	compute in reverse order	***
COCI	Bicikli	complete	tarjan scc, dp	***
DMOJ	Inaho IX	complete	matrices multiplication	****
DMOJ	Training Regimen	complete	dsu	***
DMOJ	Multiplication Madness	Fermat's little theorem	*
NA	绝对价值	complete	DSU	**
Atcoder	Knapsack 2	complete	reverse weight and value	**
DMOJ	A Subarray Problem	complete	dsu or keep upper and lower bound	**
DMOJ	City Game	complete	monotonic stack, find top and bottom bounds for a maximum length at a position	***
COCI	Index	complete	Mo's Algorithm, segment tree	***
DMOJ	Serial Killer	complete	segment tree, dp	**
DMOJ	A Rage Tree Problem	complete	segment tree, lazy propagation	***
DMOJ	Fax's Christmas Bash	complete	fenwick tree to store coefficients, binary search for convex, use ceiling or floor	****
DMOJ	Good Debugging	complete	segment tree, lazy propagation	**
NA	逆序对	complete	Mo's Algorithm, fenwick tree	***
NA	温度测量	complete	segment tree, maintain lowest temperature possible starting from some point before	***
NOI	Travel	complete	dp on DAG	**
CSP S	廊桥分配	complete	greedy	***
DMOJ	check number	complete	binary search	**
DMOJ	Arithmetic Snowman	complete	dp, be careful of memory	**
DMOJ	nightmare-a-thon	complete	segment tree	**
DMOJ	knapsack 3	complete	knapsack binary packaging	***
NOIP 18	Paving Road	complete	very standard dp	*
DMOJ	Mimi and Division	complete	partition algorithm & brute force	***
DMOJ	Frog 3	complete	Convex Hull Trick	****
UCC	WoodCutting Game	complete	game theory dp	***
DMOJ	pick up	complete	dp	**
COCI 16 c4	kas	complete	dp stores difference between two numbers	***
DMOJ	Cheapest Operation Ever	complete	Convex Hull Trick dp	****
CSP S 21	回文	complete	big brain observation	***
APIO 14	Split the Sequence	complete	Convex Hull Trick dp	****
NA	最长异或路径	complete	Trie	***
JSOI 2012	玄武密码	complete	AC automaton	****
DMOJ	Victor Makes Banks	complete	matrices power, consider case when n = 1	***
DMOJ	最小逆序对数	complete	very standard fenwick tree	**
DMOJ	School Traversal	complete	very easy and standard lca	*
DMOJ SAC	That Problem	complete	dp, memory optimization	**
DMOJ SAC	That Wall	complete	binary search, dp	***
DMOJ	Poutine	complete	lca, mantain max and second max	**
DMOJ	GGG	complete	change the index of the first array, LIS	**
DMOJ	Bruce's Little Bridge	complete	merge nodes together that don't have edge length 1	***
DMOJ	Joey and Biology	complete	shortest editing distance	**
DMOJ	Holy Grail War	complete	interval merging segment tree	***
DMOJ	Strict Evaluation	complete	basic lazy propagation	***
DMOJ	Subway_Routes	complete	locate the middle of the perimeter, and then dfs there	****
NOI 21	P1	complete	heavy light decomposition, set heavy edges as that two of the nodes have the same value, update different value every time	******
SDOI	染色	complete	combining intervals, heavy light decomposition	****
DMOJ	figurine	complete	lazy propagation, keep max for A and B, {maxA, k}, {k, maxB}	****
NA	树上操作	complete	heavy light decomposition	***
NA	最小生成树?	complete	shrink LCA(not yet implemented)	***
DMOJ	Maria and Maze	complete	don't binary search	**
NA	最大生成森林	complete	dsu, binary search	***
SCOI	游戏	complete	knapsack dp, sum to n, find number of unique LCM	****
DMOJ	2spooky4me	complete	discretization, lazy	***
DMOJ	redstone	if a node you can visit is incycle add one to amount of cycles	**
NA	JM挑数	complete	multiset	**
NA	dynamic median	complete	priority queue, one for small one for big	***
NOIP 2017	D2T3	列队	complete	splay tree
NA	Interval Reversal	complete	splay tree	*****
Another Contest 8	P5	complete	fenwick to find number of sequences	***
Another Contest 8	P3	complete	find a cycle	***
NA	网络分析	complete	dsu, dp	**
NOI 2009	Modified Treap	complete	interval dp, let w be best answer with root weight >= w, discretization, sorting	****
NA	部落战争	complete	bipartite matching	***
CTSC 2000	邱比特的烦恼	complete	KM algorithm, math	****
DMOJ	Persuation	complete	bitmask, 0x3f3f3f3f was not big enough	***
DMOJ	BST test	complete	treap	****
DMOJ	dynamic sum	complete	binary search, segment tree/block matrix too slow	***
DMOj	K-th Minimum Number	complete	merge sort segment tree	*****
CSP-S	能量项链	complete	interval dynamic programming	***
LOJ	家庭作业	complete	heap, greedy, segment tree or disjoint set union	****
TJOI	攻击装置	complete	bipartite matching, tile coloring	****
NA	合唱团	complete	dp, 1 for place at beginning, n for placing at the end	****
CPC	P4	complete	reverse graph I am so dumbbbb	**
CPC	P1	complete	turn B into 2a * 5b	**
NA	最小弹药数	complete	bipartite matching	***
VM7WC	Uniting the Earth Empire	complete	Montone stack	**
NA	棋盘覆盖	complete	hungarian algorithm bipartite matching	****
SCOI	糖果	complete	差分约束	***
ACM	The Great ATM Robbery	complete	Tarjan	****
Bulgarian OI 09	P4	complete	Monotone Stack	**
COI	Patrik	complete	Monotone Stack	**
NA	树上差分	complete	LCA, Segment Tree, lazy on tree	****
DMPG	Black and White	complete	two dimensional lazy	**
DMOJ	Subtree	complete	DP on trees, switch the root, pre-suf sum to avoid modular inverse when MOD is not prime
NA	钓鱼	complete	dynamic programming	**
ACM	数列第n项	complete	matrices, factoring	***
UTS Open 21	State Taxes	complete	block_mat, segment tree	****
UTS Open 21	Latin Class	complete	dynamic programming, prefix-sum	**
UTS Open 21	Prime Arrays	complete	Big Brain Greedy	**
DMOJ	Fibonacci hard	complete	Matrices, store big numbers as string, fast_pow in base 10 to avoid dividing strings	*****
DMOJ	Fibonacci	complete	Matrices, fast_pow	**
P3043	涂抹果酱	complete	bitmasking, dynamic programming	****
P3041	TSP 问题	complete	bitmasking, dynamic programming	***
P0414	最小瓶颈路	complete	lca	***
P3042	炮兵阵地	complete	bitmasking, dynamic programming	****
P0511	状态压缩DP	complete	bitmasking dynamic programming	****
P3036	树上最远点对	complete	LCA, Segment Tree, property of diameter of the tree	***
NA	区间lca	complete	lca, segment tree/sparse table	****
NA	次小生成树	complete	LCA, first getMax, then update x, y	****
DMOJ	dynamic range minimum query	complete	Segment Tree	*
COCI	Zapis	complete	Dynamic Programming, iomanip	***
COCI	Dostavljač	complete	Graph Theory, Dynamic Programming, knapsack problem
DMOJ	Dominos Tiling	complete	Dynamic Programming, two cases	*
DMOJ	CamelCase	complete	Dynamic Programming, unordered_set	*
NA	区间异或	complete	Segment Tree, property of xor, writing number as an array in binary	***
DMOJ	Cat Girls	complete	Dynamic Programming, Binary Search, this question is so wrong	*
NA	小白逛公园	complete	Segment Tree	**
USACO	旅馆预订	complete	Segment Tree	****
NA	47序列	complete	Segment Tree	****
NA	维护序列	complete	Segment Tree, first multiply then addition	***
NA	区间操作	complete	Segment Tree	**
NA	弱点	complete	Segment Tree, compute segment tree twice	**
NA	Interval GCD	complete	two Segment Tree, properties of GCD, be careful about absolute value	****
CCF Online	重力球	incomplete
CCF Online	吃豆人	incomplete	Prefix Sum, enumeration, greedy	****
CCF Online	切蛋糕	complete	case enumeration you need not more than three cuts	***
NOIP	魔法阵	complete	enumeration	****
CSP 2019	纪念品	complete	knapsack problem, dynamic programming	****
CSP 2019	加工零件	complete	bfs, number theory	****