Leetcode - Tree - 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.

/**
 * 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) { // 時間複雜度O(n)，空間複雜度O(sqrt(n))，如果是binarysearch Tree則爲O(lgn)
        if(root==NULL)
            return 0;
        int depthLeft=maxDepth(root->left);
        int depthRight=maxDepth(root->right);
        return depthLeft>=depthRight?depthLeft+1:depthRight+1;
    }
};