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Home/Questions/Python/Coding/Solve for the Kth smallest element in a Binary Search Tree.

Solve for the Kth smallest element in a Binary Search Tree.

Python/Codingeasy0.5 min readPremium

**Why BST Kth Smallest:** In-order traversal yields sorted order. kth smallest = kth node in in-order. Used in top-K from sorted structure, percentile queries. **Approach:** (1) In-order with counter: O(h + k) time. (2) Augmented BST: each node stores subtree size—O(h) search...

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Frequency
Low
Asked at 1 company
Category
179
questions in Python/Coding
Difficulty Split
127E|24M|28H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Expedia

Why This Question Matters

This easy-level Python/Coding question appears frequently in data engineering interviews at companies like Expedia. While less common, it tests deeper understanding that distinguishes strong candidates.

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Expert Answer
101 words

Why BST Kth Smallest: In-order traversal yields sorted order. kth smallest = kth node in in-order. Used in top-K from sorted structure, percentile queries.

Approach: (1) In-order with counter: O(h + k) time. (2) Augmented BST: each node stores subtree size—O(h) search by comparing k with left size.

Scalability: BST in-memory; for disk-backed (B-tree), similar logic. In data eng: approximate with reservoir sampling or partial sort for top-K from unsorted.

def kth_smallest(root, k):
stack = []
while root or stack:
while root:
stack.append(root)
root = root.left
root = stack.pop()
k -= 1
if k == 0: return root.val
root = root.right

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According to DataEngPrep.tech, this is one of the most frequently asked Python/Coding interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

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