[LeetCode] 230. Kth Smallest Element in a BST

轉自LeetCode

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
Output: 1

Example 2:

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

<Solution>

想法如下

• 因為 BST 的特性，用 inorder 歷遍的話，數字剛好會是從最小到最大

• 檢查目前的節點，是不是剛好就是指定的第 k 個

code 如下

Java(參考解答)

kotlin