Omenat

input/code.cpp: In function 'bool step(long long int, std::vector<int>)':
input/code.cpp:12:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < vec.size()-1; ++i) {
                     ~~^~~~~~~~~~~~~~

#include <bits/stdc++.h>

using namespace std;

#define ll long long

vector<int> vec = {};

bool ret = false;

bool step(ll sum, vector<int> vec){
    for (int i = 0; i < vec.size()-1; ++i) {
        if(vec[i] == 0) continue;
        if((sum - vec[i]) % 3 == 0 && vec.size() != 1){
            cout << vec.size()-1;
            ret = true;
            return true;
        }
        vector<int> nVec = vec;
        nVec[i] = 0;
        if(step(sum - vec[i], nVec)) return true;
    }
    return false;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int n;

    cin >> n;

    int b;

    vec.reserve(n);

    ll sum = 0;
    for (int i = 0; i < n; ++i){
        cin >> b;
        vec.emplace_back(b);
        sum += b;
    }

    sort(vec.begin(), vec.end());

    if(sum % 3 == 0){
        cout << n;
        flush(std::cout);
        return 0;
    }

    step(sum, vec);

    if(!ret){
        cout << 0;
    }

    flush(std::cout);
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: WRONG ANSWER

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 1

Verdict: WRONG ANSWER

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: WRONG ANSWER

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: WRONG ANSWER

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: WRONG ANSWER

Test 16

Group: 3

Verdict: ACCEPTED

Test 17

Group: 3

Verdict: ACCEPTED

Test 18

Group: 3

Verdict: WRONG ANSWER