problem230

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230. Kth Smallest Element in a BST (Medium)

Given the root of a binary search tree, and an integer k, return the kth (1-indexed) smallest element 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?

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).