그대, 그머가 되어 - 14496번

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내 코드

package com.company;

import java.io.*;
import java.util.*;

public class Main {
    static int a, b, N, M;
    static int count = 0;
    static boolean[] visited;
    static ArrayList<ArrayList<Integer>> list = new ArrayList<>();

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());

        a = Integer.parseInt(st.nextToken());
        b = Integer.parseInt(st.nextToken());
        st = new StringTokenizer(br.readLine());

        N = Integer.parseInt(st.nextToken());
        M = Integer.parseInt(st.nextToken());
        visited = new boolean[N + 1];

        for (int i = 0; i <= N; i++) {
            list.add(new ArrayList<>());
        }

        for (int i = 0; i < M; i++) {
            st = new StringTokenizer(br.readLine());
            int x1 = Integer.parseInt(st.nextToken());
            int x2 = Integer.parseInt(st.nextToken());
            list.get(x1).add(x2);
            list.get(x2).add(x1);
        }

        Queue<Node> pq = new PriorityQueue<>();
        pq.add(new Node(a, 0));

        while (!pq.isEmpty()) {
            Node x = pq.poll();

            if (visited[x.num])
                continue;

            visited[x.num] = true;

            if (x.num == b) {
                System.out.println(x.count);
                return;
            }

            for (int i : list.get(x.num)) {
                if (!visited[i])
                    pq.add(new Node(i, x.count + 1));
            }
        }
        System.out.println(-1);
    }
}

class Node implements Comparable<Node> {
    int num, count;

    public Node(int num, int count) {
        this.num = num;
        this.count = count;
    }

    @Override
    public int compareTo(Node o) {
        return this.count - o.count;
    }
}