Implement Deque with in-place
Last updated: September 25, 2025
Quick Overview
Implement a deque (double-ended queue) data structure that supports in-place operations for adding and removing elements from both ends in O(1) time. Your implementation should include methods for inserting and deleting elements at both the front and back of the deque. The input will consist of a series of operations, and the output should reflect the state of the deque after each operation.
Scale AI
September 25, 202537
15
3,248 solved
Implement a deque (double-ended queue) data structure that supports in-place operations for adding and removing elements from both ends in O(1) time. Your implementation should include methods for inserting and deleting elements at both the front and back of the deque. The input will consist of a series of operations, and the output should reflect the state of the deque after each operation.
This coding problem is frequently asked during Phone Screen at Scale AI. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Scale AI 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)?
- Can you solve this in a single pass?
- How would you test this solution thoroughly?
- How would your solution change if the input was sorted?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem is to implement a deque (double-ended queue) that supports O(1) operations for adding and removing elements from both ends. This data structure is best represented using a doubly linked li...
Approach
- Node Class: Create a
Nodeclass that has attributes for the value, a reference to the next node, and a reference to the previous node. - Deque Class: Create a
Dequeclass that maintai...
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