[java 백준] 실버 3/ 2606번 바이러스

https://www.acmicpc.net/problem/2606

2606번: 바이러스

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.StringTokenizer;
 
public class Main {
 
    public static int n, m;
    public static List<Integer>[] arr;
    public static boolean[] visited;
 
    public static int BFS(int n) {
 
        int cnt = 0;
        Queue<Integer> queue = new LinkedList<Integer>();
        queue.add(n);
        visited[n] = true;
 
        while (!queue.isEmpty()) {
            int node = queue.poll();
            for (int x : arr[node]) {
                if (!visited[x]) {
                    queue.add(x);
                    visited[x] = true;
                    cnt++;
                }
            }
 
        }
 
        return cnt;
    }
 
    public static void main(String[] args) throws NumberFormatException, IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st;
        int n = Integer.parseInt(br.readLine());
        int m = Integer.parseInt(br.readLine());
        arr = new ArrayList[n + 1];
        visited = new boolean[n + 1];
        for (int i = 0; i < n + 1; i++) {
            arr[i] = new ArrayList<Integer>();
 
        }
 
        for (int i = 0; i < m; i++) {
            st = new StringTokenizer(br.readLine());
            int node1 = Integer.parseInt(st.nextToken());
            int node2 = Integer.parseInt(st.nextToken());
 
            arr[node1].add(node2);
            arr[node2].add(node1);
        }
        System.out.println(BFS(1));
 
    }
 
}

 

BFS나 DFS로 풀면되는 문제이다.