Implement Skip List with in-place
Last updated: October 17, 2025
Quick Overview
Implement a Skip List data structure that supports insertion, deletion, and search operations in O(log n) time. Your implementation should allow for in-place modifications without using additional data structures for storage. The input will consist of a series of operations to perform on the Skip List, and the output should confirm the success or failure of each operation.
Instacart
October 17, 202531
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2,141 solved
Implement a Skip List data structure that supports insertion, deletion, and search operations in O(log n) time. Your implementation should allow for in-place modifications without using additional data structures for storage. The input will consist of a series of operations to perform on the Skip List, and the output should confirm the success or failure of each operation.
This coding problem is frequently asked during Technical Screen at Instacart. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Instacart expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- Can you solve this iteratively instead of recursively (or vice versa)?
- What is the worst-case input for your solution?
- What if the input doesn't fit in memory?
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Practice DSA ProblemsSample Answer
Problem Analysis
A Skip List is a probabilistic data structure that allows for efficient search, insertion, and deletion operations. It can be visualized as a multi-level linked list where each level acts as an expres...
Approach
- Structure Definition: Define a
Nodeclass that contains a value, an array of forward pointers (for different levels), and a height attribute to track its level. - Insertion: To insert a ...
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