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Linear Data StructuresIntermediate LevelStudy Time: 20 mins

Double-Ended Queue (Deque) Data Structure

A Deque (Double-Ended Queue) allows insertions and deletions at both the front and rear endpoints.

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Deque Bidirectional Operations Step-by-Step

Sample Input:Empty Deque, Operations: pushBack(20), pushFront(10), popBack()
Step 1

Push Back & Push Front

pushBack(20) puts 20 at tail. pushFront(10) puts 10 at head.

Deque State: [10 (Head), 20 (Tail)]
Items can be added to either side in O(1) time.
Step 2

Pop Back Operation

popBack() removes and returns item from tail (20).

Popped: 20 | Deque State: [10 (Head & Tail)]
Allows implementation of both Stack and Queue behaviors simultaneously.

Real-world analogy: Double-Ended Train

Double-Ended
Hover over items for details

Passengers can enter or exit from either the front engine car or the rear caboose car.

  • Double-Ended= Push & Pop available at both Head and Tail.

Operations explained

Complexity analysis

Scenario Simulator: Dataset Size (N = 500)
Presets:
N = 10N = 10,000
Complexity Curve MapDouble-Ended Queue (Deque): O(1) Constant Time
Time (t)Size N (500)N = 500O(N²)O(N log N)O(N)O(log N)O(1)Double-Ended Que
Time Steps (N=500)

1 step (Constant)

O(1) Constant Time

Space Footprint

O(N) Auxiliary Space

Memory growth rate as N expands.

Performance Rank
Optimal Tier

Relative efficiency rating for large N.

OperationTime ComplexitySpace Complexity
Push Front / BackO(1)O(1)
Pop Front / BackO(1)O(1)

Code implementations

const deque = [];
deque.unshift(10); // push front
deque.push(20);    // push back
const front = deque.shift(); // pop front

Real-world applications

Case 01

Sliding Window Solvers

Monotonic queue pattern algorithms.

Case 02

Undo/Redo Stacks

Bidirectional history managers.

Interview questions

Topic Knowledge Test & Assessment

10 Questions Assessment

Deque Knowledge & Skill Test

Validate your conceptual understanding, operation mechanics, and core concepts of Deque.