[Solved] 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.

Question

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:

kthtree1
Input: root = [3,1,4,null,2], k = 1
Output: 1

Example 2:

kthtree2
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?

Python Solution

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
def inorder(root,res,k):
    if root==None:return
    heapq.heappush(res,-root.val)
    if len(res)>k:heapq.heappop(res)
    inorder(root.left,res,k)
    inorder(root.right,res,k)

class Solution:
    def kthSmallest(self, root: TreeNode, k: int) -> int:
        res = []
        heapq.heapify(res)
        inorder(root,res,k)
        return -res[0]
Abhishek Sharma
Abhishek Sharma

Started my Data Science journey in my 2nd year of college and since then continuously into it because of the magical powers of ML and continuously doing projects in almost every domain of AI like ML, DL, CV, NLP.

Articles: 520

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