二叉树的深度

Description：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;    }}*/public class Solution {    int max = 1;    public int TreeDepth(TreeNode root) {        if (root == null) return 0;        int count = 0;        backtrack(root, count);        return max;    }        private void backtrack(TreeNode root, int count) {        if (root != null) {            count++;            if (root.left == null && root.right == null) {                max = Math.max(max, count);                return;            }            backtrack(root.left, count);            backtrack(root.right, count);        }    }}