Count Distinct SubSequences using DP

Dynamic Programming/Count Distinct Subsequences/SolutionByNeeraj.cpp

@@ -0,0 +1,42 @@
+#include <iostream>
+#include <set> 
+#include <iterator>
+#include <bitset> 
+#include <bits/stdc++.h> 
+using namespace std;
+typedef  long long int ll;
+ll mod=1000000007;
+
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(0);
+    cout.tie(0);
+    int t;
+    cin>>t;
+    while(t--) {
+        string s;
+        cin>>s;
+        int l[26] = {0};
+        int n = s.length();
+        ll sum[n+1]={0} ;
+        ll dp[n+1]={0};
+        dp[0] = 1;
+        dp[1] = 1;
+        sum[0] =1;
+        sum[1] = 2;
+        l[s[0]-'A'] = 1;
+        for(int i=2;i<=n;i++){
+            dp[i] = sum[i-1];
+            if(l[s[i-1]-'A']!=0) dp[i] = (dp[i] - sum[l[s[i-1]-'A']-1] +mod) %mod;
+            sum[i] = (sum[i-1] + dp[i] )%mod;
+            l[s[i-1]-'A'] = i;
+        }
+        ll ans =0 ;
+        for(int i=0;i<=n;i++){
+          ans = (ans + dp[i] )%mod;  
+        }
+        cout<<ans;
+    }
+    return 0;
+}