Problem:
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Breadth First Search

Write a program which reads an directed graph $G = (V, E)$, and finds the shortest distance from vertex $1$ to each vertex (the number of edges in the shortest path). Vertices are identified by IDs $1, 2, ... n$.

Input

In the first line, an integer $n$ denoting the number of vertices, is given. In the next $n$ lines, adjacent lists of vertex $u$ are given in the following format:

$u$ $k$ $v_1$ $v_2$ ... $v_k$

$u$ is ID of the vertex and $k$ denotes its degree.$v_i$ are IDs of vertices adjacent to $u$.

Constraints

$1 \leq n \leq 100$

Output

For each vertex $u$, print $id$ and $d$ in a line. $id$ is ID of vertex $u$ and $d$ is the distance from vertex $1$ to vertex $u$. If there are no path from vertex $1$ to vertex $u$, print -1 as the shortest distance. Print in order of IDs.

Sample Input 1

4
1 2 2 4
2 1 4
3 0
4 1 3

Sample Output 1

1 0
2 1
3 2
4 1

Reference

Introduction to Algorithms, Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, and Clifford Stein. The MIT Press.

Solution in JAVA (judge verdict: Accepted)

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

public class Main {
	final int INF = Integer.MAX_VALUE;

	void run() {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();

		boolean[][] g = new boolean[n][n];
		for (int i = 0; i < n; i++) {
			int u = scan.nextInt();
			int k = scan.nextInt();
			for (int j = 0; j < k; j++) {
				int v = scan.nextInt();
				g[u - 1][v - 1] = true;
			}
		}

		int time = 0;
		int[] d = new int[n];
		boolean[] isSearched = new boolean[n];
		Queue<Integer> que = new LinkedList<Integer>();

		for (int i = 0; i < n; i++)
			d[i] = INF;
		que.add(0);
		while (!que.isEmpty()) {
			int length = que.size();
			for (int i = 0; i < length; i++) {
				int id = que.poll();
				if (isSearched[id])
					continue;
				d[id] = Math.min(d[id], time);
				for (int j = 0; j < n; j++)
					if (g[id][j])
						que.add(j);
				isSearched[id] = true;
			}
			time++;
		}
		for (int i = 0; i < n; i++)
			System.out.println((i + 1) + " " + (isSearched[i] ? d[i] : -1));
	}
	public static void main(String[] args) {
		new Main().run();
	}
}