Leetcode 230 +Kth Smallest Element in a BST

Kth Smallest Element in a BST"/>

Leetcode 230 +Kth Smallest Element in a BST

Leetcode 230 +Kth Smallest Element in a BST

题目描述

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 = 13/ \1   4\2
Output: 1

Example 2:

Input: root = [5,3,6,2,4,null,null,1], k = 35/ \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?

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思路解析

    def kthSmallest(self, root: TreeNode, k: int) -> int:if root is None:return rootstack = []container = []curr = rootwhile curr or len(stack):if curr is not None:stack.append(curr)curr = curr.leftelse:node = stack.pop()container.append(node.val)if len(container) == k:breakcurr = node.rightreturn container.pop()