stack data structure: 29 MCQs with answers

Last In, First Out (LIFO)

A stack is a LIFO data structure, meaning the last element added is the first to be removed.

push

The push operation inserts an element onto the top of the stack.

pop

The pop operation removes and returns the top element of the stack.

Returns the top element without removing it

Peek (or top) returns the top element without modifying the stack.

3

Due to LIFO, the last pushed element (3) is popped first.

enqueue

Enqueue is a queue operation, not a stack operation.

A stack of plates

A stack of plates is a classic analogy: you add and remove plates from the top.

False

A stack is LIFO (Last In, First Out), not FIFO.

False

Peek returns the top element without removing it; pop removes it.

Last In, First Out

LIFO stands for Last In, First Out, which describes how the most recently added item is the first to be removed.

push(item)

The `push(item)` operation is used to add an item to the top of the stack.

Throws an exception

Calling `pop()` on an empty stack typically results in an error condition known as underflow, which may throw an exception.

Checking balanced parentheses

Stacks are commonly used to check balanced parentheses, as they follow the LIFO principle.

Returns the top item without removing it

The `peek()` operation allows you to view the top item of the stack without removing it.

By pushing the current state onto a call stack

A stack manages function calls by pushing the current state onto a call stack, allowing for proper return and recursion handling.

A linear data structure with a single open end

A stack is a linear data structure that has a single open end called the top, where all operations occur.

O(1)

The time complexity for the `push` operation in a stack is $O(1)$, meaning it takes constant time regardless of the number of elements.

isEmpty()

The `isEmpty()` operation checks whether the stack has no elements.

A stack of plates

A stack can be likened to a stack of plates, where you add and remove plates from the top, illustrating the LIFO principle.

Undo/Redo in text editors

Stacks are used to implement undo/redo features, as they naturally store actions in LIFO order.

Stack

The call stack is a stack data structure that manages function calls and returns.

O(1)

Array-based stack operations (push/pop) operate at the end of the array, which is O(1) on average.

Postfix

Postfix notation places operators after operands; stacks are used to evaluate postfix expressions.

16

Push 5, push 3, pop 5 and 3, add to get 8, push 8, push 2, pop 8 and 2, multiply to get 16.

Balanced parentheses checking

Stacks are used to check balanced parentheses by pushing opening brackets and popping on closing brackets.

It throws an underflow error

Popping from an empty stack is an underflow condition, typically resulting in an error or exception.

O(n)

A stack storing n elements requires O(n) space.

Breadth-first search

Breadth-first search uses a queue, not a stack.

Syntax analysis

Stacks are used in syntax analysis (parsing) to track nested structures and operators.