Brexit

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Stack;

public class Main {

    public static void main(String[] args) {
        IO io = new IO();
        int solmujenMaara = io.nextInt();
        int yhteyksienMaara = io.nextInt();
        int kotimaa = io.nextInt();
        int lahtija = io.nextInt();
        HashMap<Integer, Solmu> solmut = new HashMap<>();

        for (int i = 1; i <= solmujenMaara; i++) {
            solmut.put(i, new Solmu(i));
        }

        for (int i = 0; i < yhteyksienMaara; i++) {
            Solmu solmu1 = solmut.get(io.nextInt());
            Solmu solmu2 = solmut.get(io.nextInt());

            solmu1.addNeighbor(solmu2);
            solmu2.addNeighbor(solmu1);

        }

        solmut.get(kotimaa).setLahtija(true);
        solmut.get(lahtija).poistu();

        System.out.println(solmut.get(kotimaa).poistettu ? "leave" : "stay");

        io.close();
    }
}

class Solmu {

    int origneighbours;
    HashMap<Integer, Solmu> neighbours;
    boolean poistettu;
    int name;
    boolean target;
//    private int neigbours;

    public Solmu(int name) {
        this.name = name;
        neighbours = new HashMap<>();
        origneighbours = 0;
        poistettu = false;
        target = false;
    }

    public void addNeighbor(Solmu n) {
        neighbours.put(n.name, n);
        origneighbours++;
    }

    public boolean poistunko() {
        return (1.0 * neighbours.size() / origneighbours) <= 0.5;
    }

    public void poistu() {
        if (poistettu) {
            return;
        }
        poistettu = true;
        if (target) {
            return;
        }
        Stack<Solmu> moipitaamenna = new Stack<>();

        for (Solmu s : neighbours.values()) {
            if (s.poistettu) {
                continue;
            }
//            neighbours.remove(s);
            moipitaamenna.add(s);
        }
        neighbours.clear();
        while (!moipitaamenna.empty()) {
            moipitaamenna.pop().deleteNeighbor(this);
        }

    }

    public void deleteNeighbor(Solmu n) {
        neighbours.remove(n.name);
        if (poistunko()) {
            poistu();
        }
    }

    public void setLahtija(boolean l) {
        target = l;
    }

}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED

Test 31

Verdict: ACCEPTED

Test 32

Verdict: ACCEPTED

Test 33

Verdict: ACCEPTED

Test 34

Verdict: ACCEPTED

Test 35

Verdict: ACCEPTED