Queue Concept and FIFO Principle in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an element to the end of the queue.

DSA Python

queue = []
queue.[1](5)
print(queue)

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

Aappend

Bpop

Cinsert

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of append removes an element instead of adding.

Using insert adds at a specific position, not necessarily the end.

The append method adds an element to the end of the list, which simulates adding to the end of the queue.

2fill in blank

medium

Complete the code to remove the first element from the queue following FIFO.

DSA Python

queue = [1, 2, 3]
first = queue.[1](0)
print(first, queue)

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

Ainsert

Bremove

Cappend

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove removes by value, not by position.

Using append or insert does not remove elements.

The pop(0) method removes and returns the first element, following the FIFO principle.

3fill in blank

hard

Fix the error in the code to correctly dequeue an element from the queue.

DSA Python

queue = [10, 20, 30]
removed = queue.[1](0)
print(removed, queue)

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

Aremove(0)

Bpop(0)

Cdelete

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove(0) causes an error because remove expects a value, not an index.

Using delete is not a list method.

The pop(0) method removes and returns the first element, following the FIFO principle.

4fill in blank

hard

Fill both blanks to create a queue and add an element following FIFO principle.

DSA Python

queue = [1]
queue.[2](7)
print(queue)

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

A[]

Bappend

Cpop

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using {} creates a dictionary, not a queue list.

Using pop to add elements is incorrect.

Queues can be represented as lists []. Adding an element uses append to add at the end.

5fill in blank

hard

Fill all three blanks to dequeue an element and show the queue state.

DSA Python

queue = [[1]]
removed = queue.[2]([3])
print(removed, queue)

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

A10, 20, 30

Bpop

C0

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using append instead of pop to remove elements.

Using pop without index removes the last element, not the first.

The queue starts with elements 10, 20, 30. To dequeue, use pop(0) which removes the first element (index 0).

Practice

1. What does FIFO stand for in the context of a queue?

easy

A. First In, Final Output

B. Fast Input, Fast Output

C. Fast In, Fast Out

D. First In, First Out

Solution

1. Step 1: Understand FIFO meaning

   FIFO means the first element added to the queue is the first one to be removed.

2. Step 2: Match the acronym

   First In, First Out exactly matches FIFO.

3. Final Answer:

   First In, First Out -> Option D

4. Quick Check:

   FIFO = First In, First Out [OK]

Hint: Remember queue removes items in order added [OK]

Common Mistakes:

• Confusing FIFO with LIFO
• Thinking FIFO means last in first out
• Mixing up acronym meanings

2. Which of the following is the correct way to add an element '5' to a queue named q in Python using the queue.Queue module?

easy

A. q.put(5)

B. q.push(5)

C. q.enqueue(5)

D. q.add(5)

Solution

1. Step 1: Recall queue.Queue methods

   The Python queue.Queue class uses put() to add elements.

2. Step 2: Identify correct method

   enqueue(), push(), and add() are not valid methods for queue.Queue.

3. Final Answer:

   q.put(5) -> Option A

4. Quick Check:

   Use put() to add in queue.Queue [OK]

Hint: Use put() to add items in Python queue.Queue [OK]

Common Mistakes:

• Using enqueue() which is not in queue.Queue
• Using push() from stack terminology
• Using add() which is not a queue method

3. What will be the output of the following Python code using a list as a queue?

q = []
q.append(10)
q.append(20)
q.append(30)
print(q.pop(0))
print(q)

medium

A. 10
[20, 30]

B. 30
[10, 20]

C. 10
[30, 20]

D. 20
[10, 30]

Solution

1. Step 1: Understand list as queue

   Appending adds to the end: q = [10, 20, 30].

2. Step 2: pop(0) removes first element

   pop(0) removes and returns 10, leaving q = [20, 30].

3. Final Answer:

   10 [20, 30] -> Option A

4. Quick Check:

   pop(0) removes first = 10 [OK]

Hint: pop(0) removes first item in list acting as queue [OK]

Common Mistakes:

• Thinking pop() removes last item
• Confusing append with insert
• Expecting pop(0) to remove last element

4. Identify the error in the following code snippet that tries to implement a queue using a list:

q = []
q.pop()
q.append(1)
print(q)

medium

A. pop() removes last element but queue removes first

B. pop() on empty list causes error

C. append() should be before pop()

D. print() syntax is incorrect

Solution

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

   Initially q is empty, so q.pop() causes IndexError.

2. Step 2: Confirm other statements

   append(1) and print(q) are correct syntax and order does not fix pop on empty.

3. Final Answer:

   pop() on empty list causes error -> Option B

4. Quick Check:

   pop() empty list = IndexError [OK]

Hint: Don't pop from empty list; causes error [OK]

Common Mistakes:

• Ignoring empty list before pop
• Thinking pop() removes first element
• Assuming append order fixes error

5. You have a queue that initially contains [1, 2, 3]. You perform these operations:

q.append(4)
first = q.pop(0)
q.append(first * 10)
print(q)

What is the final state of the queue?

hard

A. [1, 2, 3, 4, 10]

B. [2, 3, 4, 40]

C. [2, 3, 4, 10]

D. [2, 3, 4, 1]

Solution

1. Step 1: Initial queue and append

   Start with q = [1, 2, 3]. After q.append(4), q = [1, 2, 3, 4].

2. Step 2: pop(0) removes first element

   first = q.pop(0) removes 1, so first = 1 and q = [2, 3, 4].

3. Step 3: append first * 10

   q.append(1 * 10) adds 10, so q = [2, 3, 4, 10].

4. Final Answer:

   [2, 3, 4, 10] -> Option C

5. Quick Check:

   Remove first, add 10 times it at end [OK]

Hint: Pop first, multiply, append result at end [OK]

Common Mistakes:

• Appending before popping first
• Multiplying wrong element
• Not updating queue after pop