1725H - Hot Black Hot White - CodeForces Solution

#include <bits/stdc++.h>
#define int long long
#define INT_MAX LLONG_MAX
#define INT_MIN LLONG_MIN
#define fastio(); ios_base::sync_with_stdio(false); cin.tie(NULL);
using namespace std;

int32_t main () {
    fastio();
    int t, n, rem;
    t = 1;
    while (t--) {
        cin >> n;
        vector<int> arr(n), cnt(3, 0);
        for (int i = 0; i < n; i++) {
            cin >> arr[i];
            cnt[arr[i]%3]++;
        }
        if (cnt[0] <= n/2) {
            cout << 0 << '\n';
            rem = n/2 - cnt[0];
            for (int i = 0; i < n; i++) {
                if (arr[i]%3 == 0) {
                    cout << 0;
                }
                else {
                    if (rem) {
                        cout << 0;
                        rem--;
                    }
                    else {
                        cout << 1;
                    }
                }
            }
            cout << '\n';
        }
        else if (cnt[1]+cnt[2] <= n/2) {
            cout << 2 << '\n';
            rem = n/2 - (cnt[1]+cnt[2]);
            for (int i = 0; i < n; i++) {
                if (arr[i]%3 == 1 || arr[i]%3 == 2) {
                    cout << 0;
                }
                else {
                    if (rem) {
                        cout << 0;
                        rem--;
                    }
                    else {
                        cout << 1;
                    }
                }
            }
            cout << '\n';
        }
        else {
            cout << -1 << '\n';
        }
    }
    return 0;
}