[Leetcode] 0230. Kth Smallest Element in a BST

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Table of contents

Medium

Given the root of a binary search tree, and an integer k, return the k ^th smallest value (1-indexed) of all the values of the nodes in the tree.

Example 1:

Input: root = [3,1,4,null,2], k = 1
Output: 1

Example 2:

Input: root = [5,3,6,2,4,null,null,1], k = 3
Output: 3

Constraints:

The number of nodes in the tree is n.
1 <= k <= n <= 10 ⁴
0 <= Node.val <= 10 ⁴

Follow up: If the BST is modified often (ie, we can do insert and delete operations) and you need to find the kth smallest frequently, how would you optimize?

Python

				
					# Definition for a binary tree node. from typing import List, Optional class TreeNode: def __init__(self, val=0, left=None, right=None): self.val = val self.left = left self.right = right class Solution: def addToArr(self, node: Optional[TreeNode], treeList: List[int]) -> None: if node: self.addToArr(node.left, treeList) treeList.append(node.val) self.addToArr(node.right, treeList) def kthSmallest(self, root: Optional[TreeNode], k: int) -> int: result = [] self.addToArr(root, result) return result[k-1]

Medium

Python

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