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.Scanner;
import java.util.Arrays;
import java.util.Iterator;

class Graph {
	private int totalVertex;
	private LinkedList<LinkedList<Integer>> adjList;
	private int[] bfs;
	//adjacency list of edges
	public Graph() { totalVertex = 0; }
	public void loadAdjList() {
		Scanner in = new Scanner(System.in);
		totalVertex = in.nextInt();
		adjList = new LinkedList<LinkedList<Integer>>();
		for(int i = 0; i < totalVertex; i ++) {
			LinkedList<Integer> tmp = new LinkedList<Integer>();
			int idx1 = in.nextInt() - 1;
			int degree = in.nextInt();
			//System.out.println("mark idx1 = " + idx1 + " degree = " + degree);
			for(int j = 0; j < degree; j ++) {
				int idx2 = in.nextInt() - 1;
				tmp.add(idx2);
			}	
			adjList.add(tmp);
		}
		in.close();
		bfs = new int[totalVertex];
	}
	public void BFS(int s) 
    { 
        // Mark all the vertices as not visited(By default 
        // set as false) 
        boolean visited[] = new boolean[totalVertex]; 
  
        // Create a queue for BFS 
        LinkedList<Integer> queue = new LinkedList<Integer>(); 
        LinkedList<Integer> queue2 = new LinkedList<Integer>(); 
  
        // Mark the current node as visited and enqueue it 
        visited[s]=true; 
        queue.add(s);
  
        while (queue.size() != 0) 
        { 
            // Dequeue a vertex from queue and print it 
            s = queue.poll();
            queue2.add(s);
  
            // Get all adjacent vertices of the dequeued vertex s 
            // If a adjacent has not been visited, then mark it 
            // visited and enqueue it 
            Iterator<Integer> i = adjList.get(s).listIterator(); 
            while (i.hasNext()) 
            { 
                int n = i.next(); 
                if (!visited[n]) 
                {
                    visited[n] = true; 
                    queue.add(n);
                    bfs[n] = bfs[s] + 1;
                }
                
            } 
        } 
        for(int i = 0; i < totalVertex; i++) {
        	if(i != 0 && bfs[i] == 0) bfs[i] = -1;
        }
        for(int i = 0; i < totalVertex; i++) {
        	System.out.print((i + 1) + " " + bfs[i]);
        	System.out.println();
        }
    }
}

public class Main {
	public static void main(String argv[]) {
		Graph g = new Graph();
		g.loadAdjList();
		g.BFS(0);
	}
}