[백준] 5567번 결혼식 (bfs, 구현 )

www.acmicpc.net/problem/5567

5567번: 결혼식

처음에 네트워크를 구하는 줄알고 dfs인 줄 알았으나 depth (친구의 친구)가 2인 곳까지만 탐색하므로 

bfs로 풀었다.

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class Main {
	static int n,m;
	static ArrayList<Integer>[] friend;
	static boolean[] vis;
	static int answer;
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		n=sc.nextInt();
		m=sc.nextInt();
		friend=new ArrayList[n+1];
		vis=new boolean[n+1];
		for (int i = 1; i <=n; i++) {
			friend[i]=new ArrayList<>();
		}
		for (int i = 0; i <m; i++) {
			int a=sc.nextInt();
			int b=sc.nextInt();
			friend[a].add(b);
			friend[b].add(a);
		}
		Queue<Integer> q=new LinkedList<Integer>();
		q.add(1);
		vis[1]=true;
		int depth=0;
		while(q.size()!=0) {
			int len=q.size();
			if(depth==2)break;
			for (int i = 0; i < len; i++) {
				int cur=q.poll();
				for (int k = 0; k < friend[cur].size(); k++) {
					int next=friend[cur].get(k);
					if(vis[next])continue;
					vis[next]=true;
					answer+=1;
					q.add(next);
				}
			}
			depth++;
		}
		
	
		System.out.println(answer);
	}

}