Solutions NCERT class 12 computer science chapter 4: Queue

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")

Output

MENU:

1. Add movement to the queue

2. Remove movement from the queue

3. Display current queue

4. Exit

Enter your choice (1-4): 1

Enter the movement (up/down): up

Added up to the queue

 

MENU:

1. Add movement to the queue

2. Remove movement from the queue

3. Display current queue

4. Exit

Enter your choice (1-4): 1

Enter the movement (up/down): down

Added down to the queue

 

MENU:

1. Add movement to the queue

2. Remove movement from the queue

3. Display current queue

4. Exit

Enter your choice (1-4): 3

Current queue: ['up', 'down']

 

MENU:

1. Add movement to the queue

2. Remove movement from the queue

3. Display current queue

4. Exit

Enter your choice (1-4): 2

Removed up from the queue

 

MENU:

1. Add movement to the queue

2. Remove movement from the queue

3. Display current queue

4. Exit

Enter your choice (1-4): 3

Current queue: ['down']

 

MENU:

1. Add movement to the queue

2. Remove movement from the queue

3. Display current queue

4. Exit

Enter your choice (1-4): 4

Exiting program...

 

(a) Queue

(b) FIFO

(c) enqueue, dequeue

(d) front

(e) 'A', 'S', 'D', 'F'

(f) Deque

(g)

deletionFront()

deletionRear()

deletionRear()

deletionFront()

deletionFront()

 

 

 

FIFO, First In First Out, defines a queue because in a queue, elements are retrieved from one end (called the front end) and inserted at another end (rear end). Thus, at any time, in a queue, retrieval gets the oldest element, while always adding to the rear of the queue. Thus, items are processed in first-in, first-out (FIFO) order.

 

Queues only allow insertion in one end (rear end) and retrieval from the other end (front end). A deque, on the other hand, is a double-ended queue, which allows flexibility with insertion or deletion such that one of these operations is allowed at both ends rather than having a fixed end for the operations.

 

 

 

 

 

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.")

Output

Enter a string: anupama

anupama is not a palindrome.

Enter a string: malayalam

malayalam is a palindrome.