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。

public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}

递归：

public class Solution {    public int TreeDepth(TreeNode root) {        if (root == null) return 0;        int left = TreeDepth(root.left);        int right = TreeDepth(root.right);        return Math.max(left,right) + 1;    }}

非递归：层序遍历

import java.util.LinkedList;import java.util.Queue;public class Solution {    public int TreeDepth(TreeNode root) {        if (root == null) return 0;        Queue<TreeNode> queue = new LinkedList<>();        queue.add(root);        int depth = 0;        int count = 0;        int layerCount = 1;        while (queue.size() != 0)        {            TreeNode node = queue.poll();            count++;            if (node.left != null)                queue.add(node.left);            if (node.right != null)                queue.add(node.right);                        if (count == layerCount) {                layerCount = queue.size();                depth++;                count = 0;            }        }        return depth;    }}