题目
Given a binary search tree, write a function kthSmallest
to find the kth smallest element in it.
Note: You may assume k is always valid, 1 ≤ k ≤ BST's total elements.
Example 1:
Input: root = [3,1,4,null,2], k = 1
3
/ \
1 4
\
2
Output: 1
Example 2:
Input: root = [5,3,6,2,4,null,null,1], k = 3
5
/ \
3 6
/ \
2 4
/
1
Output: 3
**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?
题目大意
给定一个二叉搜索树,编写一个函数 kthSmallest 来查找其中第 k 个最小的元素。你可以假设 k 总是有效的,1 ≤ k ≤ 二叉搜索树元素个数。
解题思路
- 由于二叉搜索树有序的特性,所以中根遍历它,遍历到第 K 个数的时候就是结果