Pop Operation on Stack in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to pop the top element from the stack.

DSA Rust

let top = stack.[1]();

Drag options to blanks, or click blank then click option'

Apop

Bpush

Cpeek

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using push instead of pop.

Using peek which only views the top element without removing it.

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

2fill in blank

medium

Complete the code to check if the stack is empty before popping.

DSA Rust

if !stack.[1]() { let top = stack.pop(); }

Drag options to blanks, or click blank then click option'

Acontains

Blen

Cis_empty

Dclear

Attempts:

3 left

💡 Hint

Common Mistakes

Using len which returns the number of elements but does not return a boolean.

Using contains which checks for a specific element.

The is_empty method returns true if the stack has no elements.

3fill in blank

hard

Fix the error in the code to safely pop an element from the stack.

DSA Rust

match stack.[1]() { Some(value) => println!("Popped: {}", value), None => println!("Stack is empty") }

Drag options to blanks, or click blank then click option'

Aremove

Bpop

Cpush

Dpeek

Attempts:

3 left

💡 Hint

Common Mistakes

Using peek which does not remove the element.

Using push which adds an element instead of removing.

The pop method returns an Option which can be Some if an element exists or None if empty.

4fill in blank

hard

Fill both blanks to pop all elements from the stack until it is empty.

DSA Rust

while !stack.[1]() { let value = stack.[2]().unwrap(); println!("Popped: {}", value); }

Drag options to blanks, or click blank then click option'

Ais_empty

Bpop

Cpeek

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using peek instead of pop to remove elements.

Using len which returns a number, not a boolean.

Use is_empty to check if the stack is empty and pop to remove the top element.

5fill in blank

hard

Fill all three blanks to pop elements from the stack and collect them into a vector.

DSA Rust

let mut popped = Vec::new(); while !stack.[1]() { if let Some(val) = stack.[2]() { popped.[3](val); } }

Drag options to blanks, or click blank then click option'

Ais_empty

Bpop

Cpush

Dpeek

Attempts:

3 left

💡 Hint

Common Mistakes

Using peek instead of pop to remove elements.

Using insert instead of push on vector.

Check if stack is empty with is_empty, remove elements with pop, and add them to vector with push.

Practice

1. What does the pop operation do in a stack data structure?

easy

A. Adds a new element to the bottom of the stack

B. Removes and returns the top element of the stack

C. Returns the bottom element without removing it

D. Clears all elements from the stack

Solution

1. Step 1: Understand stack behavior

   A stack follows Last In First Out (LIFO) principle, so the last added element is on top.

2. Step 2: Define pop operation

   The pop operation removes and returns the top element, which is the last inserted item.

3. Final Answer:

   Removes and returns the top element of the stack -> Option B

4. Quick Check:

   Pop = remove top element [OK]

Hint: Pop always removes the last added item [OK]

Common Mistakes:

• Thinking pop removes from bottom
• Confusing pop with push
• Assuming pop returns without removing

2. Which of the following is the correct Rust syntax to pop an element from a stack implemented as a Vec<T> named stack?

easy

A. let x = stack.pop_front();

B. let x = stack.remove();

C. let x = stack.pop();

D. let x = stack.delete();

Solution

1. Step 1: Recall Rust Vec methods

   Rust's Vec has a pop() method that removes and returns the last element.

2. Step 2: Check other options

   remove() requires an index, pop_front() is for other collections, delete() does not exist.

3. Final Answer:

   let x = stack.pop(); -> Option C

4. Quick Check:

   Vec pop method = stack.pop() [OK]

Hint: Use stack.pop() to remove last element in Rust Vec [OK]

Common Mistakes:

• Using pop_front() which is not in Vec
• Calling remove() without index
• Using non-existent delete() method

3. What is the output of the following Rust code?

let mut stack = vec![10, 20, 30];
let popped = stack.pop();
println!("{:?}", popped);
println!("{:?}", stack);

medium

A. Some(30)
[10, 20]

B. 30
[10, 20, 30]

C. None
[10, 20, 30]

D. Some(20)
[10, 30]

Solution

1. Step 1: Understand pop() return type

   pop() returns an Option containing the last element if present, here Some(30).

2. Step 2: Check stack after pop

   After popping 30, stack becomes [10, 20].

3. Final Answer:

   Some(30) [10, 20] -> Option A

4. Quick Check:

   pop returns Some(last element), stack shrinks [OK]

Hint: pop() returns Some(value) if not empty [OK]

Common Mistakes:

• Expecting pop() to return value directly, not Option
• Not updating stack after pop
• Confusing popped element with stack contents

4. Identify the error in this Rust code that tries to pop an element from an empty stack:

let mut stack: Vec<i32> = Vec::new();
let x = stack.pop().unwrap();
println!("{}", x);

medium

A. pop() method does not exist on Vec

B. println! macro syntax is incorrect

C. stack is not mutable

D. Calling unwrap() on None causes panic

Solution

1. Step 1: Check pop() on empty Vec

   pop() returns None if the Vec is empty.

2. Step 2: Understand unwrap() behavior

   Calling unwrap() on None causes a runtime panic (crash).

3. Final Answer:

   Calling unwrap() on None causes panic -> Option D

4. Quick Check:

   unwrap on None = panic [OK]

Hint: Avoid unwrap() on pop() without checking Some [OK]

Common Mistakes:

• Assuming pop() always returns Some
• Ignoring mut keyword needed for pop
• Misreading println! syntax

5. Given a stack implemented as Vec<i32>, how can you safely pop all elements and collect them into a new vector in reverse order without panicking?

hard

A. Use a loop with while let Some(x) = stack.pop() and push x into new vector

B. Use stack.pop().unwrap() repeatedly until empty

C. Use stack.remove(0) repeatedly to pop elements

D. Use stack.pop_front() to remove elements safely

Solution

1. Step 1: Avoid unwrap() to prevent panic

   Using unwrap() on pop() can panic if stack is empty, so avoid it.

2. Step 2: Use while let to safely pop

   Using while let Some(x) = stack.pop() safely extracts elements until empty.

3. Step 3: Push popped elements into new vector

   Each popped element x is pushed into a new vector, reversing order.

4. Final Answer:

   Use a loop with while let Some(x) = stack.pop() and push x into new vector -> Option A

5. Quick Check:

   Safe pop loop = while let Some(x) = pop() [OK]

Hint: Use while let Some(x) = pop() to avoid panic [OK]

Common Mistakes:

• Using unwrap() causing panic on empty stack
• Using remove(0) which is inefficient
• Calling pop_front() which does not exist on Vec