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: Wrong Answer)

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

public class Main {
	static int[][] matrix;
	static boolean[] visited;
	static int[] distance;
	static LinkedList<NumDis> queue;
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		
		matrix = new int[n][n];
		for (int i = 0; i < n; i++) {
			int index = sc.nextInt() - 1;
			int num = sc.nextInt();
			for (int j = 0; j < num; j++) {
				matrix[index][sc.nextInt() - 1] = 1;				
			}
		}
		
		visited = new boolean[n];
		distance = new int[n];
				
		queue = new LinkedList<NumDis>();
		queue.offer(new NumDis(0, 0));
		
		while(queue.size() > 0) {
			bfs();
		}
		
		for(int i = 0; i < n; i++) {
			System.out.printf("%1$d %2$d", i+1, distance[i]);
			System.out.println();
		}
	}
	
	public static void bfs() {
		NumDis current = queue.poll();
		int i = current.num;
		int d = current.dis;
		
		if (visited[i]) {
			return;
		}
		
		// to queue
		for(int j = 0; j < matrix[i].length; j++) {
			if (matrix[i][j] == 1) {
				queue.offer(new NumDis(j, d + 1));		
			}
		}
		
		// record
		distance[i] = d;
		visited[i] = true;
	}
	
	
}

class NumDis {
	int num;
	int dis;
	public NumDis(int num, int dis) {
		this.num = num;
		this.dis = dis;
	}
}