[백준] 2606번: 바이러스 - Java

💬 문제 파악하기

문제 출처

🔥 BFS 사용

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

public class Main {
    static int count, num, connections;
    static boolean[] visited;
    static List[] computers;
    
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        num = Integer.parseInt(br.readLine());
        connections = Integer.parseInt(br.readLine());
        visited = new boolean[num+1];
        computers = new List[num+1];
        count = 0;
        for(int i=1; i<num+1; i++) {
            computers[i] = new ArrayList<Integer>();
        }
        
        StringTokenizer st;
        for(int i=0; i<connections; i++) {
            st = new StringTokenizer(br.readLine());
            int a = Integer.parseInt(st.nextToken());
            int b = Integer.parseInt(st.nextToken());
            computers[a].add(b);
            computers[b].add(a);
        }
        
        bfs(1);
        
        System.out.println(count-1); // 시작 지점 카운트 빼주기
        br.close();
    }
    
    private static void bfs(int start) {
        Queue<Integer> queue = new LinkedList<Integer>();
        queue.add(start);
        
        while(!queue.isEmpty()) {
            int now = queue.poll();
            if(!visited[now]) {
                count++;
                visited[now] = true;
                for(int i=0; i<computers[now].size(); i++) {
                    queue.add((int)computers[now].get(i));
                }
            }
        }
    }
}

⭐️ DFS 사용

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

public class Main {
    static int count, num, connections;
    static boolean[] visited;
    static List[] computers;
    
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        num = Integer.parseInt(br.readLine());
        connections = Integer.parseInt(br.readLine());
        visited = new boolean[num+1];
        computers = new List[num+1];
        count = 0;
        for(int i=1; i<num+1; i++) {
            computers[i] = new ArrayList<Integer>();
        }
        
        StringTokenizer st;
        for(int i=0; i<connections; i++) {
            st = new StringTokenizer(br.readLine());
            int a = Integer.parseInt(st.nextToken());
            int b = Integer.parseInt(st.nextToken());
            computers[a].add(b);
            computers[b].add(a);
        }
        
        dfs(1);
        
        System.out.println(count-1); // 시작 지점 카운트 빼주기
        br.close();
    }
    
    private static void dfs(int start) {
        if(!visited[start]) {
            visited[start] = true;
            count++;
            for(int i=0; i<computers[start].size(); i++) {
                dfs((int)computers[start].get(i));
            }
        }
    }
}
}