Implement Deque with streaming input
Last updated: February 6, 2026
Quick Overview
Implement a Deque (double-ended queue) data structure that supports adding and removing elements from both ends in O(1) time. Your implementation should handle streaming input, allowing for dynamic insertion and deletion of elements as they arrive. Provide methods for adding elements to the front and back, as well as removing elements from both ends, and ensure that your solution can efficiently manage these operations.
ServiceNow
February 6, 202666
5
971 solved
Implement a Deque (double-ended queue) data structure that supports adding and removing elements from both ends in O(1) time. Your implementation should handle streaming input, allowing for dynamic insertion and deletion of elements as they arrive. Provide methods for adding elements to the front and back, as well as removing elements from both ends, and ensure that your solution can efficiently manage these operations.
This coding problem is frequently asked during Phone Screen at ServiceNow. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. ServiceNow 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 if the input doesn't fit in memory?
- Can you solve this in a single pass?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires implementing a Deque (double-ended queue) that supports O(1) time complexity for adding and removing elements from both ends. The specific pattern that applies here is the use of ...
Approach
The approach for implementing the Deque will involve creating a Node class to represent each element in the list, which will contain pointers to both the previous and next nodes. We will also maintain...
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