func_code_string: #include <bits/stdc++.h>   using namespace std;   string to_string(string s) { return     + s +    ; }   string to_string(char s) { return string(1, s); }   string to_string(const char *s) { return to_string((string)s); }   string to_string(bool b) { return (b ?  true  :  false ); }   template <typename A>   string to_string(A);   template <typename A, typename B>   string to_string(pair<A, B> p) {     return  (  + to_string(p.first) +  ,   + to_string(p.second) +  ) ;   }   template <typename A>   string to_string(A v) {     bool f = 1;     string r =  { ;     for (const auto &x : v) {       if (!f) r +=  ,  ;       f = 0;       r += to_string(x);     }     return r +  } ;   }   void debug_out() { cout << endl; }   void show() { cout << endl; }   void pret() {     cout << endl;     exit(0);   }   template <typename Head, typename... Tail>   void debug_out(Head H, Tail... T) {     cout <<     << to_string(H);     debug_out(T...);   }   template <typename Head, typename... Tail>   void show(Head H, Tail... T) {     cout << H <<    ;     show(T...);   }   template <typename Head, typename... Tail>   void pret(Head H, Tail... T) {     cout << H <<    ;     pret(T...);   }   const long long MOD = 1e9 + 7;   const long long maxn = 300000 + 10;   string s[11];   long long n, m;   bool check(string &t) {     for (long long i = 0; i < n; ++i) {       long long curr = 0;       for (long long j = 0; j < m; ++j) {         curr += (s[i][j] != t[j]);       }       if (curr > 1) return 0;     }     return 1;   }   string f() {     cin >> n >> m;     for (long long i = 0; i < n; ++i) {       cin >> s[i];     }     for (long long i = 0; i < n; ++i) {       string temp = s[i];       for (long long j = 0; j < m; ++j) {         for (long long k = 0; k < 26; ++k) {           char curr = char( a  + k);           temp[j] = curr;           if (check(temp)) {             return temp;           }         }         temp[j] = s[i][j];       }     }     return  -1 ;   }   int32_t main() {     cin.tie(0);     ios_base::sync_with_stdio(0);     ;     long long t;     cin >> t;     while (t--) {       string ans = f();       cout << ans <<   n ;     }     return 0;   }   