Split in Three

#include <bits/stdc++.h>

#define pb push_back
#define int long long
#define all(x) x.begin(), x.end()
#define ld long double
using namespace std;

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n;
    cin >> n;
    int w = n * (n + 1) / 2;
    if (w % 3) {
        cout << "IMPOSSIBLE\n";
        exit(0);
    }
    if (n % 6 == 2) {
        cout << "2 3 ";
        for (int _ = 0; _ < n / 6; _++) {
            cout << "1 2 3 3 2 1 ";
        }
    } else if (n % 6 == 3) {
        cout << "1 2 3 ";
        for (int _ = 0; _ < n / 6; _++) {
            cout << "1 2 3 3 2 1 ";
        }
    } else if (n % 6 == 5) {
        cout << "3 3 3 1 2 ";
        for (int _ = 0; _ < n / 6; _++) {
            cout << "1 2 3 3 2 1 ";
        }
    } else if (n % 6 == 0) {
        cout << "2 2 3 2 3 1 ";
        for (int _ = 0; _ < n / 6 - 1; _++) {
            cout << "1 2 3 3 2 1 ";
        }
    }

}

Test 1

Group: 1, 2

Verdict: ACCEPTED

Test 2

Group: 1, 2

Verdict: ACCEPTED

Test 3

Group: 1, 2

Verdict: ACCEPTED

Test 4

Group: 1, 2

Verdict: ACCEPTED

Test 5

Group: 1, 2

Verdict: ACCEPTED

Test 6

Group: 1, 2

Verdict: ACCEPTED

Test 7

Group: 1, 2

Verdict: ACCEPTED

Test 8

Group: 1, 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED

Test 15

Group: 2

Verdict: ACCEPTED