230. Kth Smallest Element in a BST
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Given the root of a binary search tree, and an integer k, return the kth 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 <= 1040 <= 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?
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).