a3gTDi - Online C++ Compiler & Debugging Tool

#include <bits/stdc++.h>
using namespace std;
using int64 = long long;

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

    int T;
    cin >> T;
    while(T--){
        int n;
        int64 a, b;
        cin >> n >> a >> b;
        vector<int64> c(n);
        for(int i = 0; i < n; i++)
            cin >> c[i];

        int64 g = __gcd(a, b);
        int64 C = *max_element(c.begin(), c.end());
        int64 R = C % g;

        int64 ans = 0;
        for(int i = 0; i < n; i++){
            int64 r = c[i] % g;
            int64 diff = (R - r + g) % g;
            ans = max(ans, diff);
        }

        cout << ans << "\n";
    }

    return 0;
}