my-solutions/codeforces/round-923/task-b/main.cpp

#include <iostream>

using namespace std;

string alph = "abcdefghijklmnopqrstuvwxyz";

int main() {
    int t;
    cin >> t;

    int used_chars[26];

    for (int k = 0; k < t; k++) {
        int n;
        cin >> n;

        int* s = new int[n];

        for (int i = 0; i < n; i++) {
            cin >> s[i];
        }

        for (int i = 0; i < 26; i++) {
            used_chars[i] = 0;
        }

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < 26; j++) {
                if (used_chars[j] == s[i]) {
                    cout << alph[j];
                    used_chars[j]++;
                    break;
                }
            }
        }

        cout << endl;

        delete[] s;
    }
}