STUDCOMP - buggy solution

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;

void solve() {
    int n;
    cin >> n;

    VI marks(n);
    for (auto &x : marks)
        cin >> x;
    VI app(n);
    for (auto &x : app)
        cin >> x;
    vector<PII> a(n);
    for (int i = 0; i < n; i++) {
        a[i] = {marks[i], i};
    }

    sort(a.begin(), a.end());

    vector<int> ans(n);

    set<int, greater<>> apps;
    for (int i = 0; i < n; i++) {
        int app_i = app[a[i].second];

        int size = 0;
        int sum = 0;
        for (auto x : apps) {
            sum += x;
            size += 1;
            if (sum > app_i)
                break;
        }

        apps.insert(app_i);
        ans[a[i].second] = sum > app_i ? size : -1;
    }

    for (auto x : ans)
        cout << x << " ";
}

int main() {
    solve();
    return 0;
}