Split in Three

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define per(i, a, b) for (int i = a - 1; i >= (b); --i)
#define trav(a, x) for (auto &a : x)

#define all(x) x.begin(), x.end()
#define sz(x) x.size()
#define pb push_back

#define umap unordered_map
#define uset unordered_set
#define INF 1000000000

typedef pair<int, int> ii;
typedef pair<int, ii> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef long long ll;

int main() {
    ios::sync_with_stdio(0);
    cin.tie(NULL);

    int n, tot, look, ans[101];
    memset(ans, 0, sizeof(ans));
    cin >> n;
    tot = (n + 1) * n / 2;
    if (tot % 3) {
        cout << "IMPOSSIBLE" << endl;
        return 0;
    }

    look = tot / 3;
    per(i, n + 1, 1) {
        if (look < i) continue;
        ans[i] = 2;
        look -= i;
    }

    look = tot / 3 - 1;
    per(i, n + 1, 1) {
        if (look < i || ans[i]) continue;
        ans[i] = 1;
        look -= i;
    }

    if (look) {
        cout << "IMPOSSIBLE" << endl;
        return 0;
    }
    rep(i, 1, n + 1) {
        if (!ans[i]) ans[i] = 3;
        cout << ans[i] << ' ';
    }
    return 0;
}

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: WRONG ANSWER

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