/**
 * 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:
vector<int> p;
int res = 0;
    int treeDepth(TreeNode* root) {

        dfs(0, root);

        return res;

    }
    void dfs(int u, TreeNode* root)
    {
        if(!root) 
        {
            res = max(res, u);
            return;
        }
        dfs(u + 1, root->left);
        dfs(u + 1, root->right);

    }
};