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.Linq;
using System.Collections.Generic;

namespace ALDS1_11_C
{
    class Program
    {
        static int n;
        static int[,] neighborList;
        static int[] shortestPath;
        static bool[] isVisited;


        static void Main(string[] args)
        {
            Program.n = int.Parse(Console.ReadLine());
            Program.neighborList = new int[n, n];
            Program.shortestPath = new int[n];
            Program.shortestPath[0] = 0;
            Program.isVisited = new bool[Program.n];
            Program.isVisited[0] = true;
            for (int i = 1; i < Program.n; i++)
            {
                Program.shortestPath[i] = -1;
            }
            for (int i = 0; i < Program.n; i++)
            {
                int[] tmpLine = Console.ReadLine()
                                       .Split(' ')
                                       .Select(s => int.Parse(s))
                                       .ToArray();
                for (int j = 2; j <= tmpLine[1] + 1; j++)
                {
                    Program.neighborList[tmpLine[0] - 1, tmpLine[j] - 1] = 1;
                }
            }
            Queue<int> nodeQueue = new Queue<int>();
            nodeQueue.Enqueue(1);
            while (nodeQueue.Count() > 0)
            {
                Program.BreadthFirstSearch(nodeQueue);
            }
            for (int i = 0; i < Program.n; i++)
            {
                Console.WriteLine(string.Format("{0} {1}", i + 1, Program.shortestPath[i]));
            }
        }

        static void BreadthFirstSearch(Queue<int> nodeQueue)
        {
            int tmpNode = nodeQueue.Dequeue();

            for (int i = 0; i < Program.n; i++)
            {
                if (!Program.isVisited[i] && Program.neighborList[tmpNode - 1, i] == 1)
                {
                    Program.shortestPath[i] = Program.shortestPath[tmpNode - 1] + 1;
                    Program.isVisited[i] = true;
                    nodeQueue.Enqueue(i + 1);
                }
            }

        }
    }
}