#include <iostream>
#include <stack>
using namespace std;
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 FindMaxDepth(TreeNode* root, int dep) {
        if(!root) return dep;
        return max(FindMaxDepth(root->left, dep), FindMaxDepth(root->right, dep)) + 1;
    }
    int maxDepth(TreeNode* root) {
        if(!root) return 0;
        return FindMaxDepth(root, 0);
    }
};

int main() {
    TreeNode* root = new(TreeNode);
    TreeNode* node1 = new(TreeNode);
    TreeNode* node2 = new(TreeNode);
    root->left = nullptr;
    root->right = nullptr;
    // root->left = node1;
    // root->right = node2;
    // node1->left = nullptr;
    // node1->right = nullptr;
    // node2->left = nullptr;
    // node2->right = nullptr;
    Solution obj;
    int ans = obj.maxDepth(root);
    cout<<"length = "<<ans<<endl;
}