What is the difference between a stack and a queue?

Both are linear, abstract data types, but they differ in how elements are removed: Stack (LIFO — Last In, First Out): elements are added to and removed from the same end (top). Push adds to top, pop removes from top. Like a stack of books — you can only take from the top. Use when: you need to reverse a sequence, match brackets, track function calls, handle backtracking. Queue (FIFO — First In, First Out): elements are added to the back (rear) and removed from the front. Enqueue adds to rear, dequeue removes from front. Like a queue of people — first in, first served. Use when: you need to process things in order of arrival, BFS traversal, scheduling. Key comparison: Stack = most recent first; Queue = oldest first. Both support O(1) push/enqueue and pop/dequeue. Can implement each with the other: (1) Queue using two stacks: enqueue pushes to stack1; dequeue: if stack2 empty, pop all from stack1 to stack2, then pop from stack2. Amortized O(1) per operation; (2) Stack using two queues: push to empty queue, then dequeue all from other to it. O(n) push, O(1) pop. Common interview question: implement one using the other.