【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：

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode *root) {
        if(root == NULL)
            return 0;
        if(root->left != NULL && root->right == NULL)
            return maxDepth(root->left)+1;
        if(root->right != NULL && root->left == NULL)
            return maxDepth(root->right)+1;
        int h_left = maxDepth(root->left);
        int h_right = maxDepth(root->right);
        return h_left > h_right ? h_left+1:h_right+1;
    }
};

 Java版本代码：

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxDepth(TreeNode root) {
        return maxDepthHelper(root, 0);
    }
    int maxDepthHelper(TreeNode root,int height){
        if(root == null)
            return height;
        int l = maxDepthHelper(root.left, height+1);
        int r = maxDepthHelper(root.right, height+1);
        return l > r?l:r;
    }
}