Python Program to Implement Stack using Queue

This is a Python program to implement a stack using a single queue.

The program creates a stack using a single queue and allows the user to perform push and pop operations on it.

1. Create a class Queue.
2. Define methods enqueue, dequeue, is_empty and get_size inside the class Queue.
3. Create a class Stack with instance variable q initialized to an empty queue.
4. Pushing is done by enqueuing data to the queue.
5. To pop, the queue is dequeued and enqueued with the dequeued element n – 1 times where n is the size of the queue. This causes the the last element added to the queue to reach the rear of the queue. The queue is dequeued one more time to get the item to be returned.
6. The method is_empty returns True iff the queue is empty.

Here is the source code of a Python program to implement a stack using a single queue. The program output is shown below.

class Stack:
    def __init__(self):
        self.q = Queue()
 
    def is_empty(self):
        return self.q.is_empty()
 
    def push(self, data):
        self.q.enqueue(data)
 
    def pop(self):
        for _ in range(self.q.get_size() - 1):
            dequeued = self.q.dequeue()
            self.q.enqueue(dequeued)
        return self.q.dequeue()
 
 
class Queue:
    def __init__(self):
        self.items = []
        self.size = 0
 
    def is_empty(self):
        return self.items == []
 
    def enqueue(self, data):
        self.size += 1
        self.items.append(data)
 
    def dequeue(self):
        self.size -= 1
        return self.items.pop(0)
 
    def get_size(self):
        return self.size
 
 
s = Stack()
 
print('Menu')
print('push <value>')
print('pop')
print('quit')
 
while True:
    do = input('What would you like to do? ').split()
 
    operation = do[0].strip().lower()
    if operation == 'push':
        s.push(int(do[1]))
    elif operation == 'pop':
        if s.is_empty():
            print('Stack is empty.')
        else:
            print('Popped value: ', s.pop())
    elif operation == 'quit':
        break

1. An instance of Stack is created.
2. The user is presented with a menu to perform push and pop operations on the stack.
3. The chosen operation is performed by calling the corresponding method of the stack.

Case 1:
Menu
push <value>
pop
quit
What would you like to do? push 3
What would you like to do? push 5
What would you like to do? pop
Popped value:  5
What would you like to do? pop
Popped value:  3
What would you like to do? pop
Stack is empty.
 
Case 2:
Menu
push <value>
pop
quit
What would you like to do? push 1
What would you like to do? push 2
What would you like to do? push 3
What would you like to do? push 4
What would you like to do? pop
Popped value:  4
What would you like to do? pop
Popped value:  3
What would you like to do? pop
Popped value:  2
What would you like to do? pop
Popped value:  1
What would you like to do? pop
Stack is empty.
What would you like to do? quit

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