LeetCode/230_Kth_Smallest_Element_in_a_BST.py at main · AnmolPatel20/LeetCode · GitHub

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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 <= 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?

"""

# 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
class Solution:
    def kthSmallest(self, root: Optional[TreeNode], k: int) -> int:
        n = 0
        stack = []
        cur = root

        while cur or stack:
            while cur:
                stack.append(cur)
                cur = cur.left

            cur = stack.pop()
            n += 1
            if n==k:
                return cur.val
            cur = cur.right