View difference between Paste ID: CQM09ci4 and UqvYCAJH

 #include <bits/stdc++.h>
 
 using namespace std;
 int input(){
     int res = 0; char c = ' ';
     while (c < '0') c = getchar();
     while (c >= '0') res = res * 10 + (c - '0'), c = getchar();
     return res;
 }
 const int N = 1e5 + 1, MOD = 1e9 + 7;
 
 int sum(int f, int s){
     return (f + s < MOD ? f + s : f + s - MOD);
 }
 int dif(int f, int s){
     return (f - s < 0 ? f - s + MOD : f - s);
 }
 int f[N], cnt[10], a[N], cur;
 int main(){
     int n = input();
     for (int i = 1; i <= n; ++ i){
         char c; cin >> c;
         a[i] = c - '0';
     }
     f[0] = 1;
 
     for (int i = 1, j = 1; i <= n; ++ cnt[a[i ++]]){
         while (cnt[a[i]]){
             cur = dif(cur, f[j]);
             -- cnt[a[j]], ++ j;
         }
         cur = sum(cur, f[i] = sum(cur, f[j - 1]));
     }
     cout << f[n];
 }