【leetnode刷题笔记】Maximum Depth of binary tree

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.

解题：

递归就行：根节点为空，返回0；一个子树根节点为空，另一个子树根节点不为空，就返回根节点不为空的子树高度；否则返回两个子树中高度大者加一。

代码：

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int maxDepth(TreeNode *root) {
13         if(root == NULL)
14             return 0;
15         if(root->left != NULL && root->right == NULL)
16             return maxDepth(root->left)+1;
17         if(root->right != NULL && root->left == NULL)
18             return maxDepth(root->right)+1;
19         int h_left = maxDepth(root->left);
20         int h_right = maxDepth(root->right);
21         return h_left > h_right ? h_left+1:h_right+1;
22     }
23 };

Java版本代码：

 1 /**
 2  * Definition for binary tree
 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         return maxDepthHelper(root, 0);
13     }
14     int maxDepthHelper(TreeNode root,int height){
15         if(root == null)
16             return height;
17         int l = maxDepthHelper(root.left, height+1);
18         int r = maxDepthHelper(root.right, height+1);
19         return l > r?l:r;
20     }
21 }