Stack operations (push, pop, peek) in Data Structures Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the Peek Operation

What does the peek operation do in a stack?

A Removes the bottom element of the stack

B Removes and returns the top element of the stack

C Returns the top element without removing it

D Returns the size of the stack

💡 Hint

Think about whether the element stays in the stack after the operation.

The peek operation returns the top element of the stack without removing it, allowing you to see what is on top without changing the stack.

📋 Factual

intermediate

Stack Behavior After Push and Pop

Consider an empty stack. After pushing elements 5, 10, and 15 in that order, then popping once, what is the top element?

A 5

B 10

C 15

D Stack is empty

💡 Hint

Remember that pop removes the top element.

After pushing 5, 10, 15, the stack top is 15. Popping removes 15, so the new top is 10.

🔍 Analysis

advanced

Stack Underflow Scenario

What happens if you perform a pop operation on an empty stack?

A Causes an error or exception called stack underflow

B Removes the bottom element instead

C Returns null or equivalent empty value

D Adds a default element to the stack

💡 Hint

Think about what it means to remove an element when none exist.

Trying to pop from an empty stack causes a stack underflow error because there is no element to remove.

❓ Comparison

advanced

Difference Between Push and Pop

Which statement correctly describes the difference between push and pop operations on a stack?

A Push adds a new element on top; pop removes the top element

B Both push and pop remove elements but from different ends

C Push removes the top element; pop adds a new element on top

D Push and pop both add elements but at different positions

💡 Hint

Think about how elements enter and leave the stack.

Push adds an element to the top of the stack, while pop removes the top element.

❓ Reasoning

expert

Stack State After Multiple Operations

Starting with an empty stack, the following operations are performed in order: push(3), push(7), pop(), push(9), peek(). What is the value returned by the peek operation?

A 3

B 7

C Stack is empty

D 9

💡 Hint

Track each operation step-by-step to see what remains on the stack.

After push(3) and push(7), stack top is 7. Pop removes 7, leaving 3. Push(9) adds 9 on top. Peek returns 9.