Java——求二叉树的深度

Java——求二叉树的深度

题目描述

输入一棵二叉树，求该树的深度。从根结点到叶结点依次经过的结点（含根、叶结点）形成树的一条路径，最长路径的长度为树的深度。

利用递归求解

class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
public class Solution {
    public int TreeDepth(TreeNode root) {
        if(root==null){
            return 0;
        }
        int left=TreeDepth(root.left);
        int right=TreeDepth(root.right);
        return left>right?left+1:right+1;
    }
}

利用非递归求解：利用队列（Queue）进行层次遍历

队列参考学习：https://blog.csdn.net/yangxingpa/article/month/2018/04

import java.util.Queue;
import java.util.LinkedList;
class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }
}
public class Solution {
    public int TreeDepth(TreeNode root) {
        if(root==null){
            return 0;
        }
        int deep=0,count=0,nextCount=1;
        //Queue queue=new Queue();
        //Solution.java:17: error: Queue is abstract; cannot be instantiated
        Queue queue=new LinkedList();
        queue.add(root);
        while(!queue.isEmpty()){
            TreeNode p=queue.poll();
            count++;
            if(p.left!=null){
                queue.add(p.left);
            }
            if(p.right!=null){
                queue.add(p.right);
            }
            if(count==nextCount){
                nextCount=queue.size();
                count=0;
                deep++;
            }            
        }
        return deep;
    }
}

注意点：Queue is abstract; cannot be instantiated