输入一颗树，打印“双樱桃”的个数。

一道面试题。
输入一颗树，打印“双樱桃”的个数。

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int m = sc.nextInt();
        int n = sc.nextInt();
        Map<Integer, TreeNode> map = new HashMap<>();//map来保存节点序号和节点之间的关系
        for(int i = 0; i < n; i++){
            int num1 = sc.nextInt();
            String s = sc.next();
            int num2 = sc.nextInt();
            if(!map.containsKey(num1)){
                map.put(num1, new TreeNode(num1));
            }
            if(!map.containsKey(num2)){
                map.put(num2, new TreeNode(num2));
            }
            if(s.equals("left")){
                map.get(num1).left = map.get(num2);
            }else{
                map.get(num1).right = map.get(num2);
            }
        }
        TreeNode root = map.get(1);
        Set<TreeNode> set = new HashSet<>();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);//层序遍历的方式遍历树的节点
        while(!queue.isEmpty()){
            int size = queue.size();
            for(int i = 0; i < size; i++){
                TreeNode node = queue.poll();
                if(node.left == null && node.right == null){    //叶子节点
                    set.add(node);
                }else{
                    if(node.left != null){
                        queue.add(node.left);
                    }
                    if(node.right != null){
                        queue.add(node.right);
                    }
                }

            }
        }
        int num = 0;
        for(int numt : map.keySet()){
            TreeNode node = map.get(numt);
            if(set.contains(node.left) && set.contains(node.right)){
                num ++;
            }
        }
        System.out.println(num);
    }
}
class TreeNode{//定义树的节点
    int val;
    TreeNode left;
    TreeNode right;
    public TreeNode(int val){
        this.val = val;
        this.left = null;
        this.right = null;
    }
}