Codeforces Round #603 (Div. 2)B. PIN Codes

#include <cstdio>
#include <string>
#include <iostream>
#include <map>
using namespace std;
map <string, int> M;
string s[11];
inline void change(int k) {
    M[s[k]]--;
    for (int i = 0; i <= 9; i++) {
        s[k][3] = i + ‘0‘;
        if (M[s[k]] == 0) {
            M[s[k]] = 1;
            break;
        }
    }
}
int main() {
    int n, t;
    scanf("%d", &t);
    while (t--) {
        int n;
        M.clear();
        scanf("%d", &n);
        for (int i = 0; i < n; i++) {
            cin >> s[i];
            M[s[i]]++;
        }
        int ans = 0;
        for (int i = 0; i < n; i++) {
            if (M[s[i]] > 1)
                change(i),ans++;
        }
        printf("%d\n", ans);
        for (int i = 0; i < n; i++)
            cout << s[i] << endl;
    }
    return 0;
}