func_code_string: #include <bits/stdc++.h>   using namespace std;   const int mod = 1e9 + 7, seed = 131, MAXN = 0;   struct Item {     string s;     int x;   };   int main() {     cin.tie(0);     cin.sync_with_stdio(0);     int t;     cin >> t;     while (t--) {       int n, m;       cin >> n >> m;       vector<string> arr(n);       for (int i = 0; i < n; ++i) cin >> arr[i];       queue<Item> q;       q.push({  , 0});       string str;       int curr, uwu;       for (int idx = 0; idx < m; ++idx) {         int qsize = q.size();         for (int _ = 0; _ < qsize; ++_) {           str = q.front().s;           curr = q.front().x;           q.pop();           for (char c =  a ; c <=  z ; ++c) {             uwu = 0;             for (int i = 0; i < n; ++i)               if (arr[i][idx] != c) uwu |= (1 << i);             if ((uwu & curr) == 0) q.push({str + c, uwu | curr});           }         }       }       if (q.empty())         cout << -1 <<   n ;       else         cout << q.front().s <<   n ;     }   }   