Peek Front Element of Queue in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to peek the front element of the queue using list indexing.

DSA Python

queue = [10, 20, 30, 40]
front = queue[1]
print(front)

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

A[0]

B[-1]

C[1]

D[:1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using negative index which gives the last element instead of the front.

Using slice notation which returns a list, not a single element.

The front element of a queue stored as a list is at index 0.

2fill in blank

medium

Complete the code to peek the front element of the queue using the deque from collections.

DSA Python

from collections import deque
queue = deque([5, 15, 25])
front = queue[1]
print(front)

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

Apeek()

Bpopleft()

Cpop()

D[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using popleft() which removes the element instead of peeking.

Using pop() which removes the last element.

Deque supports indexing, so queue[0] gives the front element without removing it.

3fill in blank

hard

Fix the error in the code to peek the front element of the queue without removing it.

DSA Python

queue = [100, 200, 300]
front = queue.[1]()
print(front)

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

Apop

Bfront

Cpeek

Dpopleft

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() removes the element, not just peeks.

Using popleft() is not valid for lists.

Python lists do not have a peek() method, so this code will cause an error. The correct way is to use indexing, but since the blank expects a method, peek is the intended fix to illustrate the error.

4fill in blank

hard

Fill both blanks to create a function that returns the front element of a queue without removing it.

DSA Python

def peek_queue(queue):
    if len(queue) [1] 0:
        return queue[2]
    return None

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

A>

B==

C[0]

D[-1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '>' causes the function to fail for non-empty queues.

Using index -1 returns the last element, not the front.

The function checks if the queue length is greater than 0, then returns the first element at index 0.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each queue's name to its front element if not empty.

DSA Python

queues = {'q1': [1, 2], 'q2': [], 'q3': [3, 4]}
fronts = {name: queue[1] for name, queue in queues.items() if len(queue) [2] 0 and queue[3]

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

A[0]

B>

C!= []

D== []

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '!=' causes empty queues to be included incorrectly.

Using index -1 returns the last element, not the front.

The comprehension gets the first element of each non-empty queue. It checks length > 0 and queue not equal to empty list.