Equilateral numbers

#include <bits/stdc++.h>

using namespace std;

int main()
{
	long long n;
	cin >> n;
	unordered_set<long long> set;
	long long sum = 0;
	for(long long i = 0; sum < n;i++){
		sum += i;
		set.insert(sum);
	}
	if(set.count(n) > 0){
		cout << 1 << endl;
		return 0;
	}
	for( auto x: set){
		if(set.count(n-x)>0){
			cout << 2 << endl;
			return 0;
		}
	}
	cout << 3 << endl;
	return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED