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.Linq;
using System.Collections.Generic;
using static System.Math;
using System;

public class P
{
    public int to { get; set; }
    public int step { get; set; }
}

public class hello
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        var map = new List<int>[n];
        var d = new int[n];
        for (int i = 0; i < n; i++)
        {
            d[i] = -1;
            map[i] = new List<int>();
            string[] line = Console.ReadLine().Trim().Split(' ');
            var a = int.Parse(line[0]) - 1;
            var b = int.Parse(line[1]);
            for (int j = 0; j < b; j++)
            {
                var c = int.Parse(line[j + 2]) - 1;
                map[i].Add(c);
            }
        }
        d[0] = 0;
        goDfs(map, d);
        print(d);
    }
    public static void print(int[] d)
    {
        var dL = d.Length;
        for (int i = 0; i < dL; i++)
            Console.WriteLine("{0} {1}", i + 1, d[i]);
    }
    public static void goDfs(List<int>[] map, int[] d)
    {
        var n = map.Length;
        var used = new bool[n];
        used[0] = true;
        var q = new Queue<P>();
        foreach (var x in map[0])
        {
            q.Enqueue(new P { to = x, step = 1 });
            used[x] = true;
        }
        while (q.Count() > 0)
        {
            var w = q.Dequeue();
            d[w.to] = w.step;
            foreach (var x in map[w.to])
                if (!used[x])
                {
                    q.Enqueue(new P { to = x, step = w.step + 1 });
                    used[x] = true;
                }
        }
    }
}