An Array is a linear data structure that stores elements in contiguous memory locations. Each element is accessed via an index (starting at 0). Arrays provide O(1) random access but O(n) insertion and deletion (due to shifting). They are the foundation of many other data structures and algorithms.

A Stack follows the LIFO (Last-In, First-Out) principle — the last element added is the first one removed. Think of a stack of plates: you can only add or remove from the top. Key operations: Push (add to top), Pop (remove from top), and Peek (view top without removing). All core operations are O(1).

A Queue follows the FIFO (First-In, First-Out) principle — the first element added is the first one removed. Think of a line of people waiting: the person who arrives first gets served first. Key operations: Enqueue (add to rear), Dequeue (remove from front). Both are O(1). A queue has two access points: the front (for removal) and the rear (for insertion).

Feature	Stack	Queue
Principle	LIFO (Last-In, First-Out)	FIFO (First-In, First-Out)
Insertion	Push (at top)	Enqueue (at rear)
Removal	Pop (from top)	Dequeue (from front)
Access points	One (top only)	Two (front & rear)
Analogy	Stack of plates	Waiting line / queue
Use cases	Undo/redo, recursion, parsing	Task scheduling, BFS, buffering

Array: Storing collections (e.g., contact lists, image pixels, spreadsheet rows), implementing other data structures, lookup tables.
Stack: Browser back/forward navigation, undo/redo in editors, expression evaluation, function call management (call stack), backtracking algorithms.
Queue: Printer job scheduling, BFS graph traversal, message queues in distributed systems, CPU task scheduling, IO request handling.

Array: Access O(1), Search O(n), Insert O(n), Delete O(n), Append O(1) amortized.
Stack: Push O(1), Pop O(1), Peek O(1), Search O(n). All core operations are constant time.
Queue: Enqueue O(1), Dequeue O(1), Peek O(1), Search O(n). Core operations are O(1).
Note: These assume an array-based implementation. Linked-list implementations also achieve O(1) for core operations.

Use a Stack when you need to reverse order or process the most recent items first (LIFO) — e.g., backtracking, undo functionality, depth-first search, expression parsing. Use a Queue when you need to preserve arrival order and process the oldest items first (FIFO) — e.g., task scheduling, breadth-first search, print spooling, buffering. The choice depends entirely on the access pattern your algorithm requires.

Yes! Both Stacks and Queues are abstract data types that can be implemented using arrays or linked lists. An array-based stack uses a pointer (top index) to track the top element. An array-based queue can use a circular buffer to achieve O(1) enqueue and dequeue. Many programming languages provide built-in implementations (e.g., Python's list as stack, collections.deque as queue; Java's Stack class and LinkedList as queue).

A Deque (pronounced "deck") is a double-ended queue that allows insertion and deletion at both ends. It combines the capabilities of both Stack and Queue. You can push/pop from either the front or the rear. Deques are extremely versatile — they can simulate both stacks and queues. Most programming languages offer deque implementations (e.g., Python's collections.deque, Java's ArrayDeque, C++'s std::deque).

Visualizing data structures helps build intuition about how they behave under different operations. Seeing elements shift in an Array, pop from a Stack's top, or flow through a Queue makes abstract concepts concrete. This tool lets you interact directly — insert, delete, push, pop, enqueue, and dequeue — and immediately see the results with clear visual feedback. It's ideal for students learning data structures, developers preparing for interviews, or anyone wanting to solidify their understanding.