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 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        
        int[][] g = new int[n+1][n+1];
        
        for (int i = 0; i < n; i++) {
            int u = sc.nextInt();
            int k = sc.nextInt();
            for (int j = 0; j < k; j++) {
                int v = sc.nextInt();
                g[u][v] = 1;
            }
        }
        
        int[] d = new int[n+1];
        for (int i = 0; i <= n; i++) {
            d[i] = -1;
        }
        Queue<Integer> que = new LinkedList<Integer>();
        que.add(1);
        d[1] = 0;
        while (!que.isEmpty()) {
            int top = que.poll();
            for (int j = 1; j <= n; j++) {
                if (g[top][j] == 1 && d[j] == -1) {
                    que.add(j);
                    d[j] = d[top] + 1;
                }
            }
        }
        
        for (int i = 1; i <= n; i++) {
            System.out.println(i + " " + d[i]);
        }
    }
}