Given a binary search tree, write a functionkthSmallestto find thekth smallest element in it.
Note:
You may assume k is always valid, 1 ≤ k ≤ BST's total elements.
Follow up:
What if the BST is modified (insert/delete operations) often and you need to find the kth smallest frequently? How would you optimize the kthSmallest routine?
第一種方法 中序遍歷到k 返回。 第二種遞歸。 這個新穎。但是兩次遞歸, 有點坑爹/