Program to implement queue using Stack in Python

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• program to implement queue using stack in python

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Program to implement Queue using Stack in Python

The program to implement queue using stack in python is as follows:

 

# Owner : TutorialsInhand Author : Devjeet Roy

class Queue:

    def __init__(self):
        self.stack_1 = list()
        self.stack_2 = list()

    def enqueue(self,item):
        self.stack_1.append(item)

    
    def dequeue(self):
        if len(self.stack_1) == 0 and len(self.stack_2) == 0:
            print("The Queue is empty.")

        elif len(self.stack_1) > 0 and len(self.stack_2) == 0:
            while(len(self.stack_1)):
                element = self.stack_1.pop()
                self.stack_2.append(element)
            print(self.stack_2.pop())

        else:
            print(self.stack_2.pop())
                

if __name__ == "__main__":
    q = Queue()
    q.enqueue("Apple")
    q.enqueue("Mango")
    q.enqueue("Banana")

    q.dequeue()
    q.dequeue()
    q.dequeue()
    

The output of the program to implement queue using stack is as follows:

 

PS C:\Users\DEVJEET\Desktop\tutorialsInHand> python code.py
Apple
Mango 
Banana

Few important tips about the program

1. The enqueue() operation is just about pushing the item into the first stack.

2. In case of the dequeue() method, first elements from the first stack is popped and pushed into the second stack and then removed from the second stack based on LIFO. If the first stack is empty, that means all elements from first stack has already been pushed into the second stack. So just the top of the second stack is removed.

3. The enqueue() has time complexity of O(1) and the dequeue() has that of O(n).

 

Program to implement queue using stack snapshot: