The contest starts in around ~15 minutes.

What wrong with this Replace With First's logic ?

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

int main() {
    int tt;
    cin >> tt;
    
    while (tt--) {
        int n, m;
        cin >> n >> m;
        
        string s, t;
        cin >> s >> t;
        
        if (s == t) {
            cout << 0 << endl;
            continue;
        } else if (s[0] != t[0]) {
            cout << -1 << endl;
            continue;
        } else {
            int flag = 0;
            for (int i = 0; i < min(n, m); i++) {
                if (s[i] != t[i]) {
                    flag = 1;
                    break;
                }
            }
            if (flag == 0) {
                cout << 1 << endl;
            } else {
                cout << 2 << endl;
            }
        }
    }
    return 0;
}

why is in gcd(hard) question, printing matrix with all number as 2 is wrong?

I have a question for those who solved problem Div1C (Div2D) Prefix Suffix Min Max ,

How did u figured out the solution ? did u solve almost similar problem before or solved it just now ?

i liked array concatenation (although could not solve in contest)