kth_smallest_element_in_a_bst

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230. Kth Smallest Element in a BST (Medium)

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?

Related Topics

[Tree] [Binary Search]

Similar Questions

1. Binary Tree Inorder Traversal (Medium)
2. Second Minimum Node In a Binary Tree (Easy)

Hints

Hint 1

Try to utilize the property of a BST.

Hint 2

Try in-order traversal. (Credits to @chan13)

Hint 3

What if you could modify the BST node's structure?

Hint 4

The optimal runtime complexity is O(height of BST).