[PAT] 1004 Counting Leaves （30 分）Java

A family hierarchy is usually presented by a pedigree tree. Your job is to count those family members who have no child.

Input Specification:

Each input file contains one test case. Each case starts with a line containing 0<N<100, the number of nodes in a tree, and M (<N), the number of non-leaf nodes. Then M lines follow, each in the format:

ID K ID[1] ID[2] ... ID[K]

where ID is a two-digit number representing a given non-leaf node, K is the number of its children, followed by a sequence of two-digit ID's of its children. For the sake of simplicity, let us fix the root ID to be 01.

The input ends with N being 0. That case must NOT be processed.

Output Specification:

For each test case, you are supposed to count those family members who have no child for every seniority level starting from the root. The numbers must be printed in a line, separated by a space, and there must be no extra space at the end of each line.

The sample case represents a tree with only 2 nodes, where 01 is the root and 02 is its only child. Hence on the root 01 level, there is 0 leaf node; and on the next level, there is 1 leaf node. Then we should output 0 1 in a line.

Sample Input:

2 1
01 1 02

Sample Output:

0 1

import java.util.Scanner;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
public class Main{
  
  public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int m = sc.nextInt();
    int i = 0,j,id,k,child;
    ArrayList<Integer> list;
    HashMap<Integer,ArrayList<Integer>> map = new HashMap<>();
    int[] record = new int[n];
    
    while(i < m){
      id = sc.nextInt();
      k = sc.nextInt();
      list = new ArrayList<>();
      for(j = 0;j < k;j++){
        child = sc.nextInt();
        list.add(child);
      }
      map.put(id, list);
      i++;
    }
    int p = DFS(map, record,1,0,0);
    for(i = 0; i < p ;i++){
      System.out.print(record[i] + " ");
    }
    System.out.print(record[i]);
  }
  
  private static int DFS(Map<Integer,ArrayList<Integer>> map, int[] record, int node,int level, int height){
    ArrayList<Integer> list = map.get(node);
    if(list == null){
      record[level]++;
      return height;
    }
    for(Integer integer:list){
      height = Math.max(height,DFS(map,record,integer,level+1,level+1));
    }
    return height;
  }
}