Equilateral numbers

#include <bits/stdc++.h>
using namespace std;
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
 
    long long n;
    cin >> n;
 
    auto bins = [](long long x){
        long long ans = 0;
        for(long long b=1ll<<30; b; b/=2){
            long long p = ans + b;
            if(p*(p+1)/2 <= x) ans = p;
        }
        return (ans)*(ans+1)/2;
    };
 
    int ans = 3;
    for(long long i=1; i*(i+1)/2<=n; i++){
        long long k = i*(i+1)/2;
        if(k == n){
            ans = 1;
            break;
        }
        long long m = n-k;
        long long aa = bins(m);
        if(aa == m) ans = 2;
    }
 
    cout << ans << '\n';
}

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