leetcode解题报告:104. Maximum Depth of Binary Tree

题意：

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.

难度：Easy

解题思路： 这是一道简单的深度优先搜索题目，每次只要在当前层的层数基础上加上左子树和右子树中深度最大的那一个层数就可以了。 用递归方法进行深度优先搜索遍历，算法复杂度O（n）

/**
 * 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==NULL)
            return 0;
        int l=1;
        int r=1;
        if(root->left!=NULL)
            l=1+maxDepth(root->left);
        if(root->right!=NULL)
            r=1+maxDepth(root->right);
   
        return max(l,r);
    
        
    }
};