Queue vs Stack When to Use Which in DSA Python - Compare & Choose

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Stack Operations

What is the printed output after executing these stack operations?

DSA Python

stack = []
stack.append(10)
stack.append(20)
stack.append(30)
print(stack.pop())
print(stack.pop())
stack.append(40)
print(stack.pop())

A 30\n20\n40

B 10\n20\n40

C 30\n10\n40

D 20\n30\n40

💡 Hint

Remember, stack follows Last In First Out (LIFO).

Stack adds elements to the end and removes from the end. So pop removes the last added element first.

❓ Predict Output

intermediate

Output of Queue Operations

What is the printed output after executing these queue operations?

DSA Python

from collections import deque
queue = deque()
queue.append(10)
queue.append(20)
queue.append(30)
print(queue.popleft())
print(queue.popleft())
queue.append(40)
print(queue.popleft())

A 10\n20\n30

B 20\n30\n40

C 10\n20\n40

D 30\n20\n40

💡 Hint

Queue follows First In First Out (FIFO).

Queue removes elements from the front. So popleft removes the oldest element first.

🧠 Conceptual

advanced

Choosing Between Stack and Queue

Which data structure is best suited for undo functionality in a text editor?

A Queue, because it processes elements in the order they were added.

B Stack, because it processes the most recent action first.

C Stack, because it processes elements in the order they were added.

D Queue, because it allows random access to elements.

💡 Hint

Undo needs to reverse the most recent action first.

Undo requires Last In First Out behavior, which is provided by a stack.

🧠 Conceptual

advanced

Use Case for Queue

Which scenario is best handled by a queue data structure?

A Evaluating expressions using recursion.

B Navigating back and forth in browser history.

C Reversing a string.

D Processing tasks in the order they arrive in a printer queue.

💡 Hint

Think about tasks that need to be handled in the order they come.

A printer queue processes jobs in the order they arrive, which is FIFO behavior of a queue.

🚀 Application

expert

Output of Mixed Stack and Queue Operations

Given the following code, what is the final printed output?

DSA Python

from collections import deque
stack = []
queue = deque()
stack.append(1)
stack.append(2)
queue.append(3)
queue.append(4)
print(stack.pop())
print(queue.popleft())
stack.append(queue.popleft())
print(stack.pop())

A 2\n3\n4

B 1\n3\n4

C 2\n3\n3

D 2\n4\n3

💡 Hint

Trace each operation carefully, noting which data structure is used.

Stack pops 2 first, queue pops 3 first, then 4 is appended to stack and popped.