class Solution {
public:
   /* int maxDepth(TreeNode* root) {
        // write code here
        if(!root) return 0;
        queue<TreeNode*> q;
        q.push(root);
        int hight=0;
        while(!q.empty())
        {
            ++hight;
            int n = q.size();
            for(int i=0;i<n;++i)
            {
                TreeNode* temp = q.front();
                q.pop();
                if(temp->left)
                    q.push(temp->left);
                if(temp->right)
                    q.push(temp->right);
            }
        }
        return hight;
    }*/

    int maxDepth(TreeNode* root) {
        if(root == nullptr) return 0;
        int left_hight = maxDepth(root->left) + 1;
        int right_hight = maxDepth(root->right)+1;
        return left_hight > right_hight ? left_hight : right_hight;
    }
};