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 C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace _20180319_AOJ
{
    class ALDS1_11C
    {
        static int[,] graph;
        static int[] outArr;
        static Queue<KeyValuePair<int, int>> q;
        static void Main(string[] args)
        {
            for (;;)
            {
                string line = Console.ReadLine();
                if (string.IsNullOrEmpty(line))
                {
                    break;
                }

                int n = int.Parse(line);
                graph = new int[n + 1, n + 1];
                q = new Queue<KeyValuePair<int, int>>();
                outArr = new int[n + 1];
                for (int i = 0; i < n; i++)
                {
                    int[] vertex = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
                    int u = vertex[0];
                    for (int k = 0; k < vertex[1]; k++)
                    {
                        graph[u, vertex[k + 2]] = 1;
                    }
                }

                for (int i = 0; i < outArr.Length; i++)
                {
                    outArr[i] = -1;
                }

                BreadthFirstSearch(1, 0);

                for(int i=1;i<outArr.Length;i++)
                {
                    Console.WriteLine("{0} {1}", i, outArr[i]);
                }
            }
        }

        static void BreadthFirstSearch(int id, int depth)
        {
            if (outArr[id] < 0)
            {
                outArr[id] = depth;
                for (int i = 1; i < graph.GetLength(1); i++)
                {
                    if (graph[id, i] > 0)
                    {
                        q.Enqueue(new KeyValuePair<int, int>(i, depth + 1));
                    }
                }

                while(q.Count>0)
                {
                    KeyValuePair<int, int> kvp = q.Dequeue();
                    BreadthFirstSearch(kvp.Key, kvp.Value);
                }
            }
        }
    }
}