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handheld-halting.cpp
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handheld-halting.cpp
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#include <fstream>
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
using namespace std;
vector<string> instructions;
int accumulator;
typedef enum instruction_tag {
acc,
jmp,
nop,
invalid
} tag;
tag convert_tag(string tag) {
if (tag == "acc") return acc;
if (tag == "jmp") return jmp;
if (tag == "nop") return nop;
return invalid;
}
int solve_part_one() {
unordered_set<size_t> executed;
accumulator = 0;
for (size_t i = 0; i < instructions.size(); i++) {
if (executed.find(i) != executed.end()) {
return accumulator;
}
executed.insert(i);
string instruction = instructions[i];
tag tag = convert_tag(
instruction.substr(
0, instruction.find(" ")));
int param = stoi(
instruction.substr(instruction.find(" ") + 1));
switch(tag) {
case acc:
accumulator += param;
break;
case jmp:
i += param - 1;
break;
case nop:
break;
default:
cout << "invalid instruction" << endl;
return -1;
}
}
cout << "no repeat instructions" << endl;
return -1;
}
int calculateAcc(vector<string> instructions, unordered_set<size_t> &executed) {
int accumulator = 0;
for (size_t i = 0; i < instructions.size(); i++) {
if (executed.find(i) != executed.end()) {
return accumulator;
}
executed.insert(i);
string instruction = instructions[i];
tag tag = convert_tag(
instruction.substr(
0, instruction.find(" ")));
int param = stoi(
instruction.substr(instruction.find(" ") + 1));
switch (tag) {
case acc:
accumulator += param;
break;
case jmp:
i += param - 1;
break;
case nop:
break;
default:
executed.clear();
return -1;
}
}
return accumulator;
}
int solve_part_two() {
int accumulator = 0;
for (size_t i = 0; i < instructions.size(); i++) {
string instruction = instructions[i];
tag tag = convert_tag(
instruction.substr(0, instruction.find(" ")));
if (tag == acc) continue;
vector<string> fixed = instructions;
unordered_set<size_t> executed;
if (tag == nop) {
fixed[i] = "jmp" + instruction.substr(instruction.find(" "));
} else if (tag == jmp) {
fixed[i] = "nop" + instruction.substr(instruction.find(" "));
}
accumulator = calculateAcc(fixed, executed);
if (executed.find(fixed.size() - 1) != executed.end()) break;
}
return accumulator;
}
int main() {
ifstream f;
f.open("input.txt");
string line;
while (!f.eof()) {
getline(f, line);
instructions.push_back(line);
}
cout << solve_part_one() << endl;
cout << solve_part_two() << endl;
return 0;
}