Stacks and queues are two of the most basic data structures used in programming and computer science. Both structures are linear, meaning they store elements in a sequence. However, they differ in the way elements are added, accessed, and removed.
A stack is a collection of elements with two main operations: push, which adds an element to the collection, and pop, which removes the most recently added element that was not yet removed. This is often referred to as the Last In, First Out (LIFO) principle. Think of a stack of plates: you can only take the top plate off or add a new plate to the top.
A queue is a collection of elements that supports two main operations: enqueue, which adds an element to the end of the queue, and dequeue, which removes the element from the front of the queue. This is known as the First In, First Out (FIFO) principle. An example of a queue is a line of people waiting for a service: the person who arrives first is served first.
Stacks are notably used in problems involving recursion, expression evaluation, and navigation (such as undo mechanisms in text editors). Queues are used in scheduling and processing tasks, like print spooling or order processing in online transactions.
Linked lists are often used as the underlying data structure for implementing stacks and queues due to their dynamic resizing capability. By using linked lists, we can efficiently manage the addition or removal of elements without needing to shift other elements around, as would be necessary in an array-based implementation.
Algorithms frequently utilize stacks for depth-first search implementations and postfix expression evaluations. Queues are pivotal in breadth-first search algorithms and are commonly used in scheduling algorithms to manage task execution order.