func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int t;     cin >> t;     while (t--) {       int i, n, f = 0;       cin >> n;       vector<int> v(n);       vector<int> use(n + 1, 0);       for (i = 0; i < n; i++) {         cin >> v[i];         if (v[i] < (i + 1)) {           f = 1;         }       }       if (f) {         cout <<  -1  << endl;         continue;       }       vector<int> a(n, 0);       for (i = 0; i < n; i++) {         if (!use[v[i]]) {           a[i] = v[i];           use[v[i]] = 1;         }       }       queue<int> q;       for (i = 1; i <= n; i++) {         if (!use[i]) {           q.push(i);         }       }       for (i = 0; i < n; i++) {         if (a[i] != 0) {           cout << a[i] <<    ;         } else {           cout << q.front() <<    ;           q.pop();         }       }       cout << endl;     }   }   