A queue is a first-in-first-out collection whose defining constraint is that insertion (enqueue) occurs only at the rear and removal (dequeue) only at the front, with enqueue, dequeue, front, and isEmpty all required to run in O(1) time. Implementing a queue over a singly linked list satisfies the FIFO constraint naturally, but a naive implementation fails the constant-time requirement because operations at the tail cost O(n) when the head address is the list's only retained identity; maintaining a second reference to the rear node removes that traversal and makes both ends constant-time. This belongs to the abstract-data-type layer of data structures in computer science, where the same ADT contract admits multiple concrete realizations — here the linked-list realization trades a per-node pointer overhead for the elimination of the fixed capacity, resize-and-copy cost, and pre-allocated unused memory inherent to the array (circular-buffer) realization.
A queue is a first-in-first-out collection whose defining constraint is that insertion (enqueue) occurs only at the rear and removal (dequeue) only at the front, with enqueue, dequeue, front, and isE…