[LeetCode104]Maximum Depth of Binary Tree

1. 题目来源：https://leetcode.com/problems/maximum-depth-of-binary-tree/  本题地址

   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 a binary tree node.
    * 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 == nullptr)
               return 0;
           return max(maxDepth(root->left),maxDepth(root->right)) + 1;
           
       }
   };