Maximum Depth of Binary Tree

Posted 2020-06-25 YuriFLAG

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

即求树的高度。理解这句话“path from the root node down to the farthest leaf node” 很重要。

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public int maxDepth(TreeNode root) {
12         if (root == null) {
13             return 0;
14         }
15         int result = 1;
16         return helper(root, result);
17     }
18     private int helper(TreeNode root, int result) {
19         if (root == null) {
20             return 0;
21         }
22         if (root.left == null && root.right == null) {
23             return result;
24         } else if (root.left != null && root.right == null) {
25             return helper(root.left, result + 1);
26         } else if (root.right != null && root.left == null) {
27             return helper(root.right, result + 1);
28         } else {
29             return Math.max(helper(root.left, result + 1), helper(root.right, result + 1));
30         }
31     }
32 }