func_code_string: #include <bits/stdc++.h>   using namespace std;   string str[51];   bool visited[51][51], flag = false;   int arrx[] = {1, -1, 0, 0}, arry[] = {0, 0, 1, -1}, n, m;   void dfs(int x, int y, int oldX, int oldY, char renk) {     if (x < 0 || x >= n || y < 0 || y >= m) return;     if (str[x][y] != renk) return;     if (visited[x][y] == true) {       flag = true;       return;     }     visited[x][y] = true;     for (int i = 0; i < 4; i++) {       int newX = x + arrx[i], newY = y + arry[i];       if (newX == oldX && newY == oldY) continue;       dfs(newX, newY, x, y, renk);     }   }   int main() {     cin >> n >> m;     for (int i = 0; i < n; i++) cin >> str[i];     memset(visited, 0, sizeof(visited));     for (int i = 0; i < n; i++) {       for (int j = 0; j < m; j++) {         if (!visited[i][j]) dfs(i, j, -1, -1, str[i][j]);       }     }     cout << (flag ?  Yes  :  No ) << endl;     return 0;   }   