WA on Groups but AC on CSES

[Evang264]

#include <bits/stdc++.h>
using namespace std;
template<typename T>
using minpq = priority_queue<T, vector<T>, greater<T>>;
 
const int N = 2e5+5;
int n, ans[N];
struct per {
	int l, r, id;
} a[N];
 
int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
#ifdef _DEBUG
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
	freopen("debug.txt", "w", stderr);
#endif
 
	cin >> n;
	for(int i = 0; i < n; ++i){
		cin >> a[i].l >> a[i].r;
		a[i].id = i;
	}
 
	sort(a, a+n, [](per x, per y){
		return x.l < y.l;
	});
 
	// holds rooms represented by pairs of the form (departure time, room ID)
	minpq<pair<int, int>> rooms;
	rooms.emplace(0, 1);
	for(int i = 0; i < n; ++i){
		if(rooms.top().first < a[i].l){
			ans[a[i].id] = rooms.top().second;
			rooms.pop();
		}else
			ans[a[i].id] = rooms.size() + 1;
 
		rooms.emplace(a[i].r, ans[a[i].id]);
	}
 
	cout << rooms.size() << '\n';
	for(int i = 0; i < n; ++i)
		cout << ans[i] << " \n"[i==n-1];
}

The above code works on https://cses.fi/problemset/task/1164 but not on Groups (it gets 16.7/100 points). This problem is viewable in the Week 4 homework of this semester's silver class.

[MckinleyX]

Most likely the issue happens because the problem has multiple correct answers, and CSES accepts any of them, whereas the guide grader only accepts one.

[thecodingwizard]

It's theoretically possible to implement a grader (~4 hours?). But unless this is an issue that affects many problems, it might be better to just tell students to submit their code to CSES website for now?