func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, k;   char C[3000];   long long D[3000][3000];   long long S[3000];   long long s = 0;   int main() {     cin >> n >> k;     cin >> C;     S[0] = D[0][0] = (C[0] -  a );     S[n] = D[0][n] = ( z  - C[0]);     s = D[0][k];     for (int i = 1; i < n; i++) {       int z = (i + 1) * (n - i);       D[i][0] += (C[i] -  a );       if (z <= k) D[i][z] += ( z  - C[i]);       for (int j = 0; j < i; j++) {         int z = (i - j) * (n - i);         for (int x = z; x <= k; x++) D[i][x] += ( z  - C[i]) * D[j][x - z];       }       for (int j = 0; j <= k; j++) {         D[i][j] += (C[i] -  a ) * S[j];         D[i][j] %= 1000000007;         S[j] += D[i][j];         S[j] %= 1000000007;       }       s += D[i][k];       s %= 1000000007;     }     if (k == 0) s++;     cout << s % 1000000007 << endl;     return 0;   }   