func_code_string: #include <bits/stdc++.h>   const double inf = 1e20;   using namespace std;   int n, m, i, j, f;   char a[55][55];   int vis[55][55];   int dx[4] = {1, 0, -1, 0};   int dy[4] = {0, 1, 0, -1};   void dfs(int x, int y, int oldx, int oldy) {     if (x == i && y == j && vis[i][j]) {       f = 1;       return;     }     for (int d = 0; d < 4 && !f; d++) {       int xx = x + dx[d], yy = y + dy[d];       if (a[xx][yy] == a[i][j] && xx >= 0 && yy >= 0 && xx < n && yy < m &&           !vis[xx][yy] && (oldx != xx || oldy != yy))         vis[xx][yy] = 1, dfs(xx, yy, x, y);     }   }   int main() {     cin >> n >> m;     for (i = 0; i < n; i++) cin >> a[i];     for (i = 0; i < n; i++)       for (j = 0; j < m && !f; j++) {         memset(vis, 0, sizeof(vis));         dfs(i, j, -1, -1);       }     if (f)       cout <<  Yes ;     else       cout <<  No ;     return 0;   }   