Implement Deque with in-place
Last updated: March 5, 2026
Quick Overview
Implement a deque (double-ended queue) data structure that supports in-place operations for adding and removing elements from both ends. Your implementation should include methods for adding an element to the front and back, removing an element from the front and back, and checking if the deque is empty. Ensure that all operations are performed in O(1) time complexity.
Morgan Stanley
March 5, 20269
8
687 solved
Implement a deque (double-ended queue) data structure that supports in-place operations for adding and removing elements from both ends. Your implementation should include methods for adding an element to the front and back, removing an element from the front and back, and checking if the deque is empty. Ensure that all operations are performed in O(1) time complexity.
Coding interviews at Morgan Stanley focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
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 optimize the space complexity of your solution?
- What is the worst-case input for your solution?
- How would you test this solution thoroughly?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To implement a deque (double-ended queue), we need a data structure that allows insertion and deletion of elements from both the front and the back in O(1) time. The underlying pattern here is the use...
Approach
- Node Structure: Define a
Nodeclass with properties for the value, next node, and previous node. - Deque Structure: Define a
Dequeclass that maintains pointers to the front and back...
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