Grokking 75: Top Coding Interview Questions
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Kth Smallest Element in a BST (medium)
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Problem Statement

Given the root of a binary search tree (BST) and an integer k, return the k-th smallest value in the tree.

The values in the BST are unique.

. Examples

Example 1:

  • Input: root = [5, 3, 8, 2, 4, 7, 9, 1], k = 3
      5
     / \
    3   8
   / \  / \
  2  4 7   9
 / 
 1
  • Expected Output: 3
  • Justification: The sorted order of the elements is [1, 2, 3, 4, 5, 7, 8, 9]. The 3rd smallest value is 3.

Example 2:

  • Input: root = [6, 4, 8, 2, 5, 7, 9, 1, 3], k = 5
      6
     / \
    4   8
   /\  / \
  2  5 7   9
 / \     
1   3
  • Expected Output: 5
  • Justification: The sorted order of the elements is [1, 2, 3, 4, 5, 6, 7, 8, 9]. The 5th smallest value is 5.

Example 3:

  • Input: root = [10, 5, 15, 3, 7, 13, 18, 2, 4, 6, 8], k = 6
      10
     /  \
    5    15
   /|    / \
  3 7   13 18
 /| |   |
2 4 6   8
  • Expected Output: 7
  • Justification: The sorted order of the elements is [2, 3, 4, 5, 6, 7, 8, 10, 13, 15, 18]. The 6th smallest value is 7.

Constraints:

  • The number of nodes in the tree is n.
  • 1 <= k <= n <= 10<sup>4</sup>
  • 0 <= Node.val <= 10<sup>4</sup>

Try it yourself

Try solving this question here:

Python3
Python3
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