Maximum Depth of Binary Tree 二叉樹的深度

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.

此題是經典的求二叉樹深度深度題目，可採用遞迴的方式，以此求每個節點的左子樹深度和右子樹深度，然後返回該節點左右子樹深度最大的那個即為該節點的深度

具體程式碼如下：

/**
 * 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;
            
        int nleft = maxDepth(root->left);
        int nright = maxDepth(root->right);
        
        return (nleft > nright) ? (nleft+1) : (nright+1);
    }
};