Implement Deque with O(n) time
Last updated: February 13, 2026
Quick Overview
Implement a deque (double-ended queue) data structure that supports adding and removing elements from both ends in O(n) time. 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. The input will consist of a series of operations to perform on the deque, and the output should reflect the results of those operations.
TikTok
February 13, 202632
6
1,827 solved
Implement a deque (double-ended queue) data structure that supports adding and removing elements from both ends in O(n) time. 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. The input will consist of a series of operations to perform on the deque, and the output should reflect the results of those operations.
This coding problem is frequently asked during Onsite at TikTok. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. TikTok 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
- What happens if the input contains duplicates?
- Can you optimize the space complexity of your solution?
- How would your solution change if the input was sorted?
- How would you test this solution thoroughly?
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Practice DSA ProblemsSample Answer
Problem Analysis
To implement a deque (double-ended queue) that supports adding and removing elements from both ends in O(n) time, we can use a dynamic array (like Python's list) as our underlying data structure. The ...
Approach
- Initialization: Start with an empty list to represent the deque.
- Add to Front: When adding an element to the front, insert it at index 0. If the list is full (i.e., we want to add more ...
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