Design Circular Deque
A medium-tier problem at 64% community acceptance, tagged with Array, Linked List, Design. Reported in interviews at Goldman Sachs and 0 others.
Design Circular Deque is a medium-difficulty problem that tests your ability to build a data structure from scratch, not just use one. Goldman Sachs has asked it. You need to implement a deque (double-ended queue) that wraps around a fixed-size array or linked list, supporting insertion and deletion at both ends with O(1) operations. The trick isn't the algorithm, it's tracking two pointers (front and back) correctly when the array loops. If you hit this live and panic on the wrap-around logic, StealthCoder will surface a working implementation in seconds, invisible to the proctor.
Companies that ask "Design Circular Deque"
Design Circular Deque is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderMost candidates approach this with a simple array and fail when they try to shrink or expand it cleanly. The winning move is a circular buffer: a fixed-size array where front and back pointers wrap modulo the array length. You track size separately to distinguish 'full' from 'empty'. The pitfall is off-by-one errors when adding or removing at either end, and incorrectly computing the next valid index. Some use a linked list instead, which avoids the modulo math but costs O(1) space per node. Either works; the interviewer cares that you reason through edge cases (empty on pop, full on push) and explain why circular matters. If you've only ever used deques and never built one, StealthCoder is the hedge for the live OA.
Pattern tags
You know the problem.
Make sure you actually pass it.
Design Circular Deque recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Design Circular Deque interview FAQ
Is this actually asked at big tech companies?+
Yes. Goldman Sachs has reported it. It's a classic design interview problem because it forces you to think about memory layout and pointer management without hiding behind a library. Mid-level candidates often blank on the wrap-around logic under pressure.
What's the real difference between using an array vs. a linked list here?+
Array-based (circular buffer) is faster and more space-efficient, but requires careful modulo arithmetic and tracking two pointers. Linked list avoids the modulo dance and handles resizing naturally, but uses more memory and has worse cache locality. Interviewers usually accept either, but array-based is more impressive.
What's the trick to handling wrap-around correctly?+
Use modulo consistently: next index is (current + 1) % capacity. Track size separately from pointers so you can tell full (size == capacity) from empty (size == 0). Most errors come from forgetting to update size on push/pop or from misallocating the array.
How long should this take to code in an interview?+
15 to 20 minutes if you've seen it before. 25 to 35 minutes if you're reasoning through it cold. The design is straightforward once you pick array or linked list; the bulk of time goes to edge cases and debug-testing all four operations (push front, push back, pop front, pop back).
Will I actually need to build this in a real job?+
Rarely. But interviewers use it to test your ability to reason about data structure invariants and handle pointers or indices correctly. It's less about the deque itself and more about showing you can code carefully under pressure.
Want the actual problem statement? View "Design Circular Deque" on LeetCode →