func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     bool flag = true;     int n, m;     cin >> n;     cin >> m;     char prev;     for (int i = 0; i < n; i++) {       string row;       cin >> row;       if (i != 0 && row[0] == prev) {         flag = false;       }       for (int j = 1; j < m; j++) {         if (row[j] != row[0]) {           flag = false;           break;         }       }       prev = row[0];     }     if (flag) {       cout <<  Yes  << endl;     } else {       cout <<  No  << endl;     }     return 0;   }   