func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long N = 1000;   bool fg[55][55];   long long n, m, dy[4] = {1, 0, -1, 0}, dx[4] = {0, 1, 0, -1};   bool flag;   char s[55][55];   void dfs(long long x, long long y, long long st, long long ed) {     fg[x][y] = true;     for (long long i = 0; i < 4; i++) {       long long a = x + dx[i], b = y + dy[i];       if (a >= 1 && a <= n && b >= 1 && b <= m && s[a][b] == s[x][y] &&           (st != a || ed != b)) {         if (fg[a][b]) {           flag = true;           break;         }         dfs(a, b, x, y);       }     }   }   signed main() {     memset(fg, false, sizeof fg);     cin >> n >> m;     flag = false;     for (long long i = 1; i <= n; i++) scanf( %s , s[i] + 1);     for (long long i = 1; i <= n; i++) {       for (long long j = 1; j <= m; j++) {         if (!fg[i][j]) {           fg[i][j] = true;           dfs(i, j, i, j);           if (flag) break;         }       }       if (flag) break;     }     if (flag)       cout <<  Yes ;     else       cout <<  No ;     return 0;   }   