Omenat

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

const int mx = 1e5 + 1;
ll dp[mx][3], arr[mx], n;

ll f(ll i, ll mod) {
  if (dp[i][mod]) return dp[i][mod];
  if (i == n) return mod == 0 ? 0 : -1;
  dp[i][mod] = f(i + 1, mod);
  ll next = f(i + 1, (mod + arr[i]) % 3);
  if (next != -1)
    dp[i][mod] = max(dp[i][mod], next + 1);
  return dp[i][mod];
}

int main() {
  memset(dp, 0, sizeof(dp));
  cin >> n;

  for (int i = 0; i < n; ++i) {
    cin >> arr[i];
  }

  cout << f(0, 0);
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 1

Verdict: ACCEPTED

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