func_code_string: #include <bits/stdc++.h>   #pragma comment(linker,  /STACK:102400000,102400000 )   using namespace std;   template <class T, class U>   inline void Max(T &a, U b) {     if (a < b) a = b;   }   template <class T, class U>   inline void Min(T &a, U b) {     if (a > b) a = b;   }   inline void add(int &a, int b) {     a += b;     while (a >= 1000000007) a -= 1000000007;   }   int pow(int a, int b) {     int ans = 1;     while (b) {       if (b & 1) ans = ans * (long long)a % 1000000007;       a = (long long)a * a % 1000000007;       b >>= 1;     }     return ans;   }   char s[5010];   int dp[5010][5010], ne[5010][26], f[5010], inv[5010], sum[5010];   int C(int a, int b) {     return 1LL * f[a] * inv[a - b] % 1000000007 * inv[b] % 1000000007;   }   int main() {     int T, i, j, k, ca = 0, m, K = 0, n;     scanf( %d%s , &n, s);     f[0] = 1;     for (int i = 1; i < n + 1; i++) f[i] = f[i - 1] * (long long)i % 1000000007;     inv[n] = pow(f[n], 1000000007 - 2);     for (int i = n - 1; i >= 0; i--)       inv[i] = inv[i + 1] * (long long)(i + 1) % 1000000007;     int last[26] = {0};     memset(last, -1, sizeof(last));     sum[0] = 1;     for (int i = 1; i < n + 1; i++) {       int c = s[i - 1] -  a ;       for (int j = i + 1 - 1; j >= 1; j--) {         if (last[c] != -1) {           dp[i][j] = (sum[j - 1] - dp[last[c]][j - 1] + 1000000007) % 1000000007;           sum[j] = (0LL + sum[j] + dp[i][j] - dp[last[c]][j] + 1000000007) %                    1000000007;         } else {           dp[i][j] = sum[j - 1];           add(sum[j], dp[i][j]);         }       }       last[c] = i;     }     int ans = 0;     for (int i = 1; i < n + 1; i++)       if (sum[i]) {         add(ans, 1LL * sum[i] * C(n - 1, i - 1) % 1000000007);       }     printf( %d n , ans);     return 0;   }   