Implement Stack using Queues Python

PROGRAM TO IMPLEMENT STACK USING QUEUES

from queue import Queue

  

class Stack:

      

    def __init__(self):

          

        # Two inbuilt queues 

        self.q1 = Queue()

        self.q2 = Queue() 

              

        # To maintain current number 

        # of elements

        self.curr_size = 0

  

    def push(self, x):

        self.curr_size += 1

  

        # Push x first in empty q2 

        self.q2.put(x) 

  

        # Push all the remaining 

        # elements in q1 to q2. 

        while (not self.q1.empty()):

            self.q2.put(self.q1.queue[0]) 

            self.q1.get()

  

        # swap the names of two queues 

        self.q = self.q1 

        self.q1 = self.q2 

        self.q2 = self.q

  

    def pop(self):

  

        # if no elements are there in q1 

        if (self.q1.empty()): 

            return

        self.q1.get() 

        self.curr_size -= 1

  

    def top(self):

        if (self.q1.empty()):

            return -1

        return self.q1.queue[0]

  

    def size(self):

        return self.curr_size

  

# Driver Code 

if __name__ == '__main__':

    s = Stack()

    s.push(1) 

    s.push(2) 

    s.push(3) 

  

    print("current size: ", s.size())

    print(s.top()) 

    s.pop() 

    print(s.top()) 

    s.pop() 

    print(s.top()) 

  

    print("current size: ", s.size())




OUTPUT:

current size: 3
3
2
1
current size: 1

CREDITS: https://www.geeksforgeeks.org/implement-stack-using-queue/