class Solution {
private:
    int i = 0;
public:
    TreeNode* kthNode(TreeNode* root, int k) {
        if(root != NULL){
            TreeNode *left = NULL, *right = NULL;
            if(root->left)
                left = kthNode(root->left, k);
            i++;
            if(i == k)
                return root;
            if(root->right)
                right = kthNode(root->right, k);
            return left == NULL ? right : left;
        }

    }
};