题目链接/文章讲解/视频讲解： https://programmercarl.com/0104.%E4%BA%8C%E5%8F%89%E6%A0%91%E7%9A%84%E6%9C%80%E5%A4%A7%E6%B7%B1%E5%BA%A6.html

1.先完成递归，二刷再完善

CPP

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int getMax(TreeNode *node){//后序遍历求高度，根节点高度即为叶子结点深度
        if(node == NULL)return 0;
        int leftDepth = getMax(node->left);
        int rigthDepth = getMax(node->right);
        int res = 1 + max(leftDepth,rigthDepth);
        return res;
    }
    int maxDepth(TreeNode* root) {
        return getMax(root);
    }
};