Omenat

input/code.cpp: In function 'bool step(long long int, std::vector<int>, int)':
input/code.cpp:20:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < vec2.size(); ++i) {
                     ~~^~~~~~~~~~~~~

#include <bits/stdc++.h>

using namespace std;

#define ll long long

vector<int> vec = {};

bool ret = false;

bool step(ll sum, vector<int> vec2, int amount){
    for (int i : vec2) {
        if(i == 0) continue;
        if((sum - i) % 3 == 0){
            cout << amount;
            ret = true;
            return true;
        }
    }
    for (int i = 0; i < vec2.size(); ++i) {
        if(vec2[i] == 0) continue;
        vector<int> nVec = vec2;
        nVec[i] = 0;
        if(step(sum - vec2[i], nVec, amount - 1)) 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;
    }

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

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

    step(sum, vec, n-1);

    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: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED

Test 16

Group: 3

Verdict: ACCEPTED

Test 17

Group: 3

Verdict: ACCEPTED

Test 18

Group: 3

Verdict: ACCEPTED