Which data structure is best suited for LIFO (last in, first out) semantics?

• A. Queue
• B. Stack
• C. Graph
• D. Hash table

Answer: (B)

LIFO semantics mean the last item you add should be the first one you take back. A stack provides exactly that behavior: you push elements onto the top and pop them off from the top, so the most recently added item is the first to be removed. Operating on a stack often includes push to add, pop to remove, and peek or top to view the next item without removing it. This structure naturally models processes like a function call stack or undo functionality, where you need to revert to the most recent action first.

A queue, by contrast, follows a first-in, first-out order, so the oldest item is removed first, not the most recent. A graph is a set of nodes connected by edges and isn’t about a single removal order. A hash table stores key-value pairs with no inherent order of removal. Therefore, for true last-in, first-out behavior, the best choice is a stack.