2047B.cpp

#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < (n); i++)

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t; cin >> t;
    while (t--) {
        int n; cin >> n;
        string s; cin >> s;

        map<char, int> freq;
        for (char ch : s) {
            freq[ch]++;
        }

        // Find character with max and min frequency
        char maxChar = s[0], minChar = s[0];
        int maxFreq = 0, minFreq = INT_MAX;

        for (auto &[ch, count] : freq) {
            if (count > maxFreq) {
                maxFreq = count;
                maxChar = ch;
            }
            if (count <= minFreq ) {
                minFreq = count;
                minChar = ch;
            }
        }

        // Replace the first occurrence of minChar with maxChar
        rep(i, n) {
            if (s[i] == minChar) {
                s[i] = maxChar;
                break;
            }
        }
        cout << s << "\n";
    }

    return 0;
}