백준, 2623, 그래프, 음악프로그램

Problem2623.java

import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

/**
 * 백준, 2623, 그래프
 * 음악프로그램 
 * 
 * @author whitebeard-k
 *
 */
public class Problem2623 {

	static int N;
	static int M;
	static int[][] link;
	static LinkedList<Integer>[] list;
	static int[] in;

	@SuppressWarnings("unchecked")
	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		N = sc.nextInt();
		M = sc.nextInt();

		in = new int[N + 1];
		link = new int[N + 1][N + 1];

		list = new LinkedList[N + 1];
		for (int i = 1; i <= N; i++)
			list[i] = new LinkedList<>();

		for (int i = 0; i < M; i++) {

			int size = sc.nextInt();
			int from = sc.nextInt();

			for (int k = 1; k < size; k++) {
				int to = sc.nextInt();

				if (link[from][to] == 0) {
					link[from][to] = 1;
					list[from].add(to);
					in[to]++;
				}

				from = to;
			}
		}

		sc.close();

		StringBuffer buffer = new StringBuffer();

		Queue<Integer> queue = new LinkedList<>();
		for (int i = 1; i <= N; i++) {
			if (in[i] == 0) {
				queue.add(i);
				buffer.append(i).append("\n");
			}
		}

		if (queue.isEmpty()) {
			System.out.println(0);
			return;
		}

		while (!queue.isEmpty()) {

			int from = queue.poll();

			for (int to : list[from]) {

				if (link[from][to] == 1) {
					if (--in[to] == 0) {
						queue.add(to);
						link[from][to] = 0;
						buffer.append(to).append("\n");
					}
				}
			}
		}

		for (int i = 1; i <= N; i++) {
			if (in[i] != 0) {
				System.out.println(0);
				return;
			}
		}

		System.out.println(buffer.toString());
	}
}