Code : Bessie and MEX

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

#define endl "\n"

void solve(vector<int> &a) {
    int n = a.size();

    vector<int> p(n);
    int mex = n;
    for (int i = n - 1; i >= 0; i--) {
        p[i] = mex - a[i];
        mex = min(mex, p[i]);
    }
    for (int i = 0; i < n; i++) {
        cout << p[i] << " ";
    }
    cout << endl;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int t;
    cin >> t;
    for (int zz = 0; zz < t; zz++) {
        int n;
        cin >> n;
        vector<int> a(n);
        for (int i = 0; i < n; i++) {
            cin >> a[i];
        }
        solve(a);
    }
    return 0;
}