Omenat

import java.util.*;

// tiedetään, huono mutta idgaf

public class a {
public static void main(String[] args) {
	IO io = new IO();
	
	int n = io.nextInt();
	LinkedList<Integer> o = new LinkedList<>();
	int t = 0;
	for (int i = 0; i < n ; i++) {
	  int s = io.nextInt();
	  if (s % 3 == 0) {
	    t++;
	  } else {
	    o.add(s);
	  }
	}
	ListIterator<Integer> i = o.listIterator();
	LinkedList<Integer> z = new LinkedList<>();
	long j = 0;
	int k = 0;
	while(i.hasNext()) {
		int q = i.next();
		j += q;
		k++;
		if (j  % 3 == 0) {
			t += k;
			 j =k = 0;
			z.clear();
		} else 
			z.add(q);
	}
	while (!z.isEmpty() && haku(z, 0)) {
		t++;
	}
	
	io.println(t);
	
	io.close(); // TÄYTYY KUTSUA LOPUKSI, muuten tuloste voi jäädä kirjoittamatta
}
static boolean haku(LinkedList<Integer> z, long s) {
	if (z.isEmpty()) return false;
	int a = z.pollLast();
	if (haku(z, s + a)) return true;
	if (haku(z, s)) return true;
	z.addLast(a);
	return false;
}
}

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: WRONG ANSWER

Test 6

Group: 1

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: WRONG ANSWER

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: WRONG ANSWER

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