Equilateral numbers

#include <iostream>
#include <cmath>
using namespace std;
typedef long long ll;
ll nums[1<<20];

bool test(ll n) {
	ll x = (sqrtl(1+8*n)-1)/2;
	if (x*(x+1)/2==n) return 1;
	if (x*(x-1)/2==n) return 1;
	if ((x+1)*(x+2)/2==n) return 1;
	return 0;
}

int main() {
	ll n;
	cin>>n;
	if (test(n)) {
		cout<<"1\n";
		return 0;
	}
	for(ll i=1; ; ++i) {
		ll a = i*(i+1)/2;
		if (a>n) {
			cout<<"3\n";
			return 0;
		}
		if (test(n-a)) {
			cout<<"2\n";
			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