Question

What are the differences between a linked list and a stack?

Short answer

Linked lists are node-based structures allowing flexible access, while stacks are LIFO structures with restricted access to the last element added.

Step-by-step solution

Understand Definitions

A linked list is a data structure consisting of nodes where each node contains data and a reference to the next node in the sequence. A stack, on the other hand, is a collection of elements that supports last-in, first-out (LIFO) access. Understanding these definitions helps in identifying their inherent differences.

Identify Structural Differences

In a linked list, each element points to the next, allowing for dynamic sizing and easy insertion or removal at any position. A stack does not inherently point to the next element but rather uses operations like 'push' (add an element) and 'pop' (remove an element) to manage order.

Explore Operational Differences

Linked lists allow accessing and modifying elements anywhere in the list, while stacks restrict access to the last added element only. This restriction means that a stack is a specialized type of data structure that emphasizes the order of operations.

Consider Use Cases

Linked lists are preferred when elements need to be frequently inserted or deleted. They are often used for implementing stacks, queues, etc. Stacks are used in scenarios such as function call management in programming languages (execution stack), backtracking algorithms, or undo mechanisms in applications.

Key concepts

Linked List

In the world of data structures, a **linked list** is a fascinating structure that consists of a sequence of elements, known as nodes. Each node in a linked list contains two important components:

• Data that holds the actual value;
• A reference, or a pointer, to the next node in the sequence.

This structure allows the linked list to grow and shrink dynamically. It enables dynamic memory allocation which means its size can change during program execution depending on the operations being performed.
This differs from data structures like arrays, which have a fixed size. To insert or remove nodes in a linked list, you simply adjust the pointers in the nodes, making operations such as insertion and deletion quite efficient in comparison to other data structures which require shifting elements.

Stack

A **stack** is a fundamental data structure often compared to a deck of cards. You can think of it as a collection that organizes elements based on their order of entry. New elements are added to the top of the stack, and only the element at the top can be removed. This makes the stack operate in a specific order, known as LIFO.
You might wonder how a stack is built and used. Internally, it can be implemented using arrays or linked lists, depending on the complexity you wish to achieve. Using arrays can mean fixed memory usage, while a linked list implementation can give you the flexibility of dynamic sizing. This flexibility makes stacks incredibly useful in scenarios where the order of operations is crucial, such as managing the execution context in programming languages or undo functionality in software applications.

LIFO access

The essence of a **LIFO access** mechanism is the notion of order. Last-In, First-Out (LIFO) is a pattern that dictates the way elements are added and removed from a collection. In a LIFO system, the most recently added element is the first to be removed. Picture stacking plates: you add new plates on top and remove the top plate first. This behavior seamlessly models certain computational processes.
LIFO is central to the functioning of a stack. The primary operations are 'push' (to add an element to the top) and 'pop' (to remove the element from the top). This ensures all operations occur at one end of the stack, which can be particularly useful for algorithms requiring reverse order processing or in managing recursive function calls.

Dynamic Sizing

**Dynamic sizing** refers to a data structure's ability to adjust its size during runtime. Linked lists and stacks (when implemented with linked lists) excel in offering this capability. Dynamic sizing allows a data structure to expand as it stores more elements, or shrink if elements are removed. In a linked list, for instance, adding a new element means creating a new node and linking it to the existing sequence, without the hassle of resizing an entire structure, as would be required with arrays.
This flexibility makes data structures with dynamic sizing adaptable and efficient for varying data loads, offering performance advantages in many applications. It is particularly beneficial for stacks that dynamically adjust in response to the number of operations whist maintaining the required order and efficiency in accessing elements.