func_code_string: #include <bits/stdc++.h>   using namespace std;   int n;   char s[200010], t[200010];   double s1[200010][26], s2[200010][26];   double ans = 0.0;   int main() {     scanf( %d n , &n);     memset(s1, 0, sizeof(s1));     memset(s2, 0, sizeof(s2));     for (int i = 1; i <= n; i++) {       scanf( %c , &s[i]);       for (int c = 0; c < 26; c++) s1[i][c] = s1[i - 1][c];       s1[i][s[i] -  A ] += i;     }     scanf(  n );     for (int i = 1; i <= n; i++) {       scanf( %c , &t[i]);       for (int c = 0; c < 26; c++) s2[i][c] = s2[i - 1][c];       s2[i][t[i] -  A ] += i;     }     scanf(  n );     double total = 0.0;     for (int i = 1; i <= n; i++) {       total += 1.0 * i * i;       ans += 1.0 * (s2[i - 1][s[i] -  A ]) * (n - i + 1);       ans += 1.0 * (s1[i - 1][t[i] -  A ]) * (n - i + 1);       if (t[i] == s[i]) ans += 1.0 * i * (n - i + 1);     }     double ret = ans / total;     printf( %.12lf n , ret);     return 0;   }   