/**
 * 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:
    //将每一层都遍历到,记录下最大层
    int max = 0;
    void dfs(TreeNode *root, int d){
        if(!root){
            if(d > max)
                max = d;
            return ;
        }
        dfs(root->left, d + 1);
        dfs(root->right, d + 1);
    }

    int treeDepth(TreeNode* root) {
        int d = 0;
        dfs(root, d);
        return max;
    }
    //取巧做法
    // int treeDepth(TreeNode* root) {
    //     if(!root) return 0;
    //     return max(treeDepth(root->left), treeDepth(root->right)) + 1;
    // }
};