백준 2606번

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

2606번: 바이러스

 

풀이

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.Arrays;

public class Main {

	public static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
	public static BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));
	
	public static ArrayList<Integer> arr[];
	public static boolean visited[];
	public static int cnt = 0;
	
	public static void main(String[] args) throws Exception {
		int n = Integer.parseInt(reader.readLine());
		int m = Integer.parseInt(reader.readLine());
		
		arr = new ArrayList[n + 1];
		visited = new boolean[n + 1];
		
		for (int i = 1; i <= n; i++) {
			arr[i] = new ArrayList<Integer>();
		}
		
		for (int i = 0; i < m; i++) {
			int xy[] = Arrays.stream(reader.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
			int x = xy[0];
			int y = xy[1];
			
			arr[x].add(y);
			arr[y].add(x);
		}
		
		for (int i = 1; i <= n; i++) {
			arr[i].sort(null);
			visited[i] = false;
		}
		
		dfs(1);
		writer.write(cnt - 1 + "");
		writer.flush();
	}
	
	public static void dfs(int v) throws IOException {
		if (visited[v] == true) {
			return;
		} else {
			cnt++;
			visited[v] = true;
			for (int i = 0; i < arr[v].size(); i++) {
				dfs(arr[v].get(i));
			}
		}
	}
}