[백준 2606] 바이러스 (실버 3) 문제 풀이- 자바 Java

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1. DFS 풀이

import java.util.*;

class Main {
    static boolean[][] graph;
    static boolean[] visited;
    static int N, M;
    static int answer;

    public static void dfs(int idx) {
        visited[idx] = true;
        answer++;
        for (int i = 1; i <= N; i++)
            if (visited[i] == false && graph[idx][i])
                dfs(i);
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        N = sc.nextInt();
        M = sc.nextInt();

        graph = new boolean[N + 1][N + 1];
        visited = new boolean[N + 1];

        int x, y;
        for (int i = 0; i < M; i++) {
            x = sc.nextInt();
            y = sc.nextInt();
            graph[x][y] = graph[y][x] = true;
        }

        dfs(1);

        System.out.println(answer - 1);
        sc.close();
    }
}