Class 12 Computer Science Chapter 4 Queue – NCERT Solutions & Answers

NCERT Solutions Class 12 Computer Science Chapter 4 Queue (2025-26)

1. Fill in the blank

1. ____________ is a linear list of elements in which insertion and deletion takes place from different ends.
2. Operations on a queue are performed in __________ order.
3. Insertion operation in a queue is called __________ and deletion operation in a queue is called ____________.
4. Deletion of elements is performed from __________ end of the queue.
5. Elements ‘A’,’S’,’D’ and ‘F’ are present in the queue, and they are deleted one at a time, ________________ is the sequence of element received.
6. ___________ is a data structure where elements can be added or removed at either end, but not in the middle.
7. A deque contains ‘z’,’x’,’c’,’v’ and ‘b’. Elements received after deletion are ‘z’,’b’,’v’,’x’ and ‘c’. ________________ is the sequence of deletion operation performed on deque.

1. Answer: Queue
2. Answer: FIFO
3. Answer: enqueue, dequeue
4. Answer: front
5. Answer: ‘A’, ‘S’, ‘D’, ‘F’
6. Answer: Deque
7. Answer: deletionFront(), deletionRear(), deletionRear(), deletionFront(), deletionFront()

2. Compare and contrast queue with stack.

Answer: A queue operates on the First-In-First-Out (FIFO) principle, where insertion (enqueue) happens at the rear and deletion (dequeue) at the front. In contrast, a stack works on Last-In-First-Out (LIFO) principle, with both insertion (push) and deletion (pop) at the top end. Thus, a queue is like a line, while a stack is like a pile.

3. How does FIFO describe queue?

Answer: FIFO (First-In-First-Out) means the element inserted earliest in the queue is removed first. In a queue, elements are always added at the rear and removed from the front, so the oldest element exits before newer ones, following FIFO order.

4. Write a menu driven Python program using queue, to implement movement of shuttlecock in its box.

Answer:

queue = []

def display_queue():
    if not queue:
        print("Queue is empty")
    else:
        print("Current queue:", queue)

def enqueue(item):
    queue.append(item)

def dequeue():
    if queue:
        removed = queue.pop(0)
        print("Removed", removed, "from the queue")
    else:
        print("Queue is empty, cannot remove")

while True:
    print("\nMENU:")
    print("1. Add movement to the queue")
    print("2. Remove movement from the queue")
    print("3. Display current queue")
    print("4. Exit")
    choice = input("Enter your choice (1-4): ")

    if choice == '1':
        movement = input("Enter the movement (up/down): ")
        enqueue(movement)
        print("Added", movement, "to the queue")
    elif choice == '2':
        dequeue()
    elif choice == '3':
        display_queue()
    elif choice == '4':
        print("Exiting program...")
        break
    else:
        print("Invalid choice, please try again")

5. How is queue data type different from deque data type?

Answer: A queue allows insertion at one end (rear) and removal from the other end (front) only. Deque (double-ended queue) allows insertion and deletion from both ends, providing more flexibility in handling data from either end.

6. Show the status of queue after each operation:

• enqueue(34)
• enqueue(54)
• dequeue()
• enqueue(12)
• dequeue()
• enqueue(61)
• peek()
• dequeue()
• dequeue()
• dequeue()
• dequeue()
• enqueue(1)

Answer:

• [] → [34]
• [34] → [34, 54]
• [34, 54] → [54]
• [54] → [54, 12]
• [54, 12] → [12]
• [12] → [12, 61]
• [12, 61] → PEEK = 12
• [12, 61] → [61]
• [61] → []
• [] → Underflow (queue empty)
• [] → Underflow (queue empty)
• [] → [1]

7. Show the status of deque after each operation:

• peek()
• insertFront(12)
• insertRear(67)
• deletionFront()
• insertRear(43)
• deletionRear()
• deletionFront()
• deletionRear()

Answer:

• [] → peek = Queue empty
• [] → [12]
• [12] → [12, 67]
• [12, 67] → [67]
• [67] → [67, 43]
• [67, 43] → [67]
• [67] → []
• [] → Underflow (deque empty)

8. Write a Python program to check whether the given string is palindrome or not, using deque. (Hint : refer to algorithm 4.1)

Answer:

def Deque():
    return []

def addRear(deque, ch):
    deque.append(ch)

def removeFront(deque):
    if len(deque) == 0:
        return None
    return deque.pop(0)

def removeRear(deque):
    if len(deque) == 0:
        return None
    return deque.pop()

def palchecker(aString):
    chardeque = Deque()
    for ch in aString:
        addRear(chardeque, ch)
    while len(chardeque) > 1:
        first = removeFront(chardeque)
        last = removeRear(chardeque)
        if first != last:
            return False
    return True

string1 = input("Enter a string: ")
pal = palchecker(string1.lower())
if pal:
    print(string1, "is a palindrome.")
else:
    print(string1, "is not a palindrome.")

NCERT Solutions Class 12 Computer Science Chapter 4 Queue – Key Concepts and Benefits

Mastering queue and deque data structures from the NCERT Solutions Class 12 Computer Science Chapter 4 Queue (2025-26) builds a solid programming foundation. These concepts are essential for coding interviews and CBSE board exams.

Focus on practice with FIFO operations and Python implementation. By working through the NCERT exercises, students improve logical thinking and hone skills necessary for real-world problem-solving.

Review exercise-based solutions regularly to reinforce your learning and boost your exam strategy. Consistent practice of these solutions will help you secure high marks in your CBSE Class 12 board exams.