[JAVA/백준] DFS와 BFS: 바이러스

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import java.util.Scanner;

/**
 * @author HEESOO
 *
 */
public class Main {
	static int[][] graph;
	static boolean[] visit;
	static int cnt;
	public static void dfs(int n) {
		if(visit[n]) return;
		
		visit[n]=true;
		cnt++;
		for(int i=1;i<visit.length;i++) {
			if(graph[n][i]==1&&!visit[i])
				dfs(i);
		}
		
	}
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scan = new Scanner(System.in);
		int n=scan.nextInt();
		int m=scan.nextInt();
		graph=new int[n+1][n+1];
		visit=new boolean[n+1];
		for(int i=0;i<m;i++) {
			int x=scan.nextInt();
			int y=scan.nextInt();
			graph[x][y]=1;
			graph[y][x]=1;
		}
		
		cnt=0;
		dfs(1);
		System.out.println(cnt-1);
	}
}