Problem:
MathJax.Hub.Config({ tex2jax: { inlineMath: [["$","$"], ["\\(","\\)"]], processEscapes: true }});

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: Wrong Answer)

import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.*;

public class Main {
    static Map<Integer, int[]> map = new HashMap<Integer, int[]>();
    static Map<Integer, Boolean> visited = new HashMap<Integer, Boolean>();
    static List<Integer> que = new ArrayList<Integer>();

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

        for (int i = 0; i < n; i++){
            String[] s = br.readLine().split(" ");
            int u = Integer.parseInt(s[0]);
            int k = Integer.parseInt(s[1]);
            int[] a = new int[k];
            for (int j = 0; j < k; j++){
                a[j] = Integer.parseInt(s[j+2]);
            }
            map.put(u, a);
            visited.put(u, false);
        }

        int[] d = new int[n + 1];
        int v = 1;
        que.add(v);
        visited.put(1, true);
        int step = 0;
        while (que.size() > 0){
            //System.out.println(que);
            v = que.remove(0);
            d[v] = step;    
            //add nextVerts to the que
            try{
                if (map.get(v) != null){
                    int[] nextArr = map.get(v);
                
                    boolean flag = false;
                    for (int j = 0; j < nextArr.length; j++){
                        if (visited.get(nextArr[j])){
                            ;
                        }else{
                            //System.out.println(que + " " +nextArr[j]+ " " +visited.get(nextArr[j])+ " " + "nextArr"+step);
                            que.add(nextArr[j]);
                            flag = true;
                            visited.put(nextArr[j], true);
                        }
                    }
                    if (flag){step++;}
                }
            }catch (NullPointerException e){
                e.printStackTrace();
                
            }
        }
            
        for (int i = 1; i < n + 1; i++){
            System.out.println(i + " " + d[i]);
        }
    }    
}