Split in Three

input/code.cpp:64:7: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main () {
       ^

#include <bits/stdc++.h>
//#pragma GCC optimize "O3"
///if ((double) ((double)(clock() - cl)/(double)CLOCKS_PER_SEC)>1.85) { break;}
#include <ext/pb_ds/assoc_container.hpp>
#define int long long
#define double long double
#define ft first
#define sc second
#define pb push_back
#define e '\n'
#define booost ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0); cerr.tie(0);
#define all(x) (x).begin(),(x).end()
#define file(x) freopen(string(string((x)) + ".in").c_str(), "r", stdin); freopen(string(string((x)) + ".out").c_str(), "w", stdout);
#define GG cout << " OPA " << '\n';

using namespace std;
using namespace __gnu_pbds;

typedef pair <int, int> pi;
typedef tree <pi, null_type, less<pi>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

const int N = 20 + 5;
const int K = 10;
const int KK = 20;
const int INF = 1e18;
const double d_INF = 2000000000.0;
const double EPS = 1e-17;
const int MOD = 1e9 + 7;
const int LOG = 30;

void solve() {
    int n;
    cin >> n;
    int sum = (n + 1) * n / 2;
    if (sum % 3 != 0) {cout << "IMPOSSIBLE\n"; return;}
    sum /= 3;
    sum --;
    set <int> m;
    for (int i = 1; i <= n; i ++) {
        m.insert(i);
    }
    map <int, int> mp;
    map <int, int> used;
    int need = sum;
    for (int i = n; i >= 1; i --) {
        if (used[i] || i > need) continue;
        mp[i] = 1;
        used[i] = 1;
        need -= i;
    }
    need = sum + 1;
    for (int i = n; i >= 1; i --) {
        if (used[i] || i > need) continue;
        mp[i] = 2;
        used[i] = 1;
        need -= i;
    }
    for (int i = 1; i <= n; i ++) {
        if (!mp[i]) cout << 3 << ' ';
        else cout << mp[i] << ' ';
    }
}
main () {
    int test = 1;
    booost;
//    cin >> test;
    while (test --) {
        solve();
    }
}

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