백준 1976번 여행 가자

package test;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.StringTokenizer;

public class BaekJoonQ1976 {
	static BufferedWriter bw;
	static int id[] = null;

	static int root(int node) {
		while (id[node] != node) {
			id[node] = id[id[node]];
			node = id[node];
		}
		return node;
	}

	static void union(int firstNode, int secNode) {
		int valueFirst = root(firstNode);
		int valueSec = root(secNode);
		if (valueFirst != valueSec) {
			id[valueFirst] = valueSec;
		}
	}

	static boolean isConnected(int firstNode, int secNode) {
		return root(firstNode) == root(secNode);
	}

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		bw = new BufferedWriter(new OutputStreamWriter(System.out));
		StringTokenizer st;

		int city = Integer.parseInt(br.readLine());
		int plan = Integer.parseInt(br.readLine());

		id = new int[city + 1];
		for(int i=0;i<=city;i++) {
			id[i] =i;
		}
		for (int i = 1; i <= city; i++) {
			st = new StringTokenizer(br.readLine());
			for (int j = 1; j <= city; j++) {
				int connection = Integer.parseInt(st.nextToken());

				if (connection == 1) {
					union(i, j);
				}

			}
		}
		st = new StringTokenizer(br.readLine());
		int trip = Integer.parseInt(st.nextToken());
		boolean flag = true;

		for (int i = 1; i < plan; i++) {
			flag = flag && isConnected(trip, Integer.parseInt(st.nextToken()));
		}

		bw.write(flag ? "YES" : "NO");
		bw.flush();
	}

}