[Leetcode] 0230. Kth Smallest Element in a BST

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內容目錄

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 <= 10⁴
0 <= Node.val <= 10⁴

Follow up: If the BST is modified often (i.e., 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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