Linked List
A linked list is a linear data structure made up of nodes, where each node stores a value and a reference (pointer) to the next node in the sequence, allowing efficient insertion and removal without shifting other elements.
Definition
A linked list is a linear data structure made up of nodes, where each node stores a value and a reference (pointer) to the next node in the sequence, allowing efficient insertion and removal without shifting other elements.
Overview
Unlike an array, which stores elements in contiguous memory and allows constant-time indexed access, a linked list stores each element in its own node scattered in memory, connected only by pointers — trading away fast random access for cheap insertion and deletion anywhere in the sequence, since adding or removing a node just means updating a couple of pointers rather than shifting every subsequent element. This makes linked lists a natural fit whenever a program frequently inserts or removes items from the middle or front of a sequence, at the cost of O(n) time to reach an arbitrary position, since traversal must follow pointers one node at a time. Common variants include singly linked lists (each node points only to the next), doubly linked lists (each node points to both the next and previous node, allowing traversal in either direction), and circular linked lists (the last node points back to the first). Linked lists also form the conceptual foundation for other structures: stacks and queues are frequently implemented on top of linked lists, and understanding node-and-pointer traversal is a prerequisite for grasping more advanced structures like trees and graphs. Linked lists are a staple of introductory computer science courses precisely because they force students to reason explicitly about pointers, memory references, and recursion (many linked-list operations are naturally recursive), and analyzing their operations is a common early exercise in applying Big O notation. In practice, modern high-level languages often favor dynamic arrays for general-purpose sequences due to better cache locality, but linked lists remain important both pedagogically and in specific scenarios like implementing certain queues, undo histories, and low-level memory-constrained systems. It is often mentioned alongside Data Structures in this space.
Key Concepts
- Nodes store a value plus a pointer/reference to the next node
- O(1) insertion and deletion given a reference to the position
- O(n) access time to reach an arbitrary position (no random access)
- Variants: singly linked, doubly linked, and circular linked lists
- Foundation for implementing stacks, queues, and other structures
- Contrasts with arrays' contiguous memory and fast indexed access
Use Cases
Frequently Asked Questions
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