A deque, short for double-ended queue, lets you add and remove at both ends. Push and pop work on the front and on the back. It is a queue and a stack fused into one structure.
That is exactly what a plain stack or queue cannot do. A stack only touches one end. A queue adds at one end and removes at the other. Neither gives you free access to both ends at once.
This both-end access shows up in real work. Sliding-window scans, work-stealing schedulers, and browser history all rely on it. When a single end is not enough, a deque is the natural next step.
Rewriting in plainer words…
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If a deque can do everything a stack or queue can, why not use it everywhere?A narrower type states intent and blocks misuse, like popping the wrong end. Pick the smallest interface the code needs.
What you can say
A deque, short for double-ended queue, lets you push and pop at both the front and the back.
So it's really a stack and a queue fused into one structure.
A stack only works at one end, and a queue adds at one end and removes at the other, so neither gives you both ends at once.
You see it in sliding-window scans, work-stealing schedulers and browser history, where the code needs to work both ends.
I reach for one when a single end isn't enough, but if the code only needs LIFO or FIFO, a plain stack or queue makes the intent clearer.
Weak answers to avoid
Mixes up deque with the dequeue operationDequeue is the act of removing from a queue. A deque is a whole structure. Say 'double-ended queue' once so the interviewer knows you mean the structure.
Lists operations with no reason to carePush and pop at both ends is the minimum. Add one case where a single end falls short, such as a sliding-window scan, to show you know when to use it.
Implies it's fast anywhere, not just at the endsOnly the two ends are cheap. Inserting or removing in the middle is still O(n) in common implementations, so be precise about 'both ends'.
Interview lens
Likely follow-ups, what you can say, and the weak answers to avoid.
