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.io.*;
import java.util.*;

class Main{
  static int count = 0;
  static int a = 1;
  static int[] list;

  final static int INF = 100;

  public static void main(String[] args)throws IOException{
    BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
    int n = Integer.parseInt(bf.readLine());
    int[][] G = new int[n+1][n];
    int[] d = new int[n+1];

    list = new int[n+1];

    for(int i=0 ; i<n ; i++){
      String[] str = bf.readLine().split(" ");
      int x = Integer.parseInt(str[0]);
      int y = Integer.parseInt(str[1]);
      d[x] = -1;

      for(int j=0 ; j<y ; j++){
        G[x][j] = Integer.parseInt(str[j+2]);
      }
    }

    d[1] = 0;
    list[0] = 1;

    search(G, d);

    for(int i=1 ; i<=n ; i++){
      System.out.println(i + " " + d[i]);
    }

  }

  static void search(int[][] G, int[] d){
    for(;count<a ; count++){
      int fr = list[count];

      for(int i=0 ; i<G[fr].length ; i++){
        int v = G[fr][i];
        if(d[v] == -1){
          d[v] = d[fr] + 1;
          list[a++] = v;
        }
      }
    }
  }
}