Stack Using 2 Queues.py

"""
----------------------------------------- Stack Using 2 Queues -------------------------------------------

You need to implement a Stack class using two queues as its data members.

Only 2 data members should be there inside the class - two queues, which should be created dynamically and 
both should be public. Use the inbuilt queue.

Implement the following public functions :

1. Constructor -
    Initialises both the data members.

2. push :
    This function should take one argument of type T and has return type void. This function should insert 
    an element in the stack. Time complexity should be O(1).

3. pop :
    This function takes no input arguments and has return type T. This should removes the last element 
    which is entered and return that element as an answer.

4. top :
    This function takes no input arguments and has return type T. This should return the last element 
    which is entered and return that element as an answer.

5. getSize :
    Return the size of stack i.e. count of elements which are present ins stack right now. Time complexity 
    should be O(1).
"""

import queue
class StackUsingQueues:
    
    def __init__(self):
        self.q1 = queue.Queue()
        self.q2 = queue.Queue()
        
        
    def push(self,data):
        self.q1.put(data)
        

    def pop(self):
        if self.q1.empty():
            return -1
        while self.q1.qsize() != 1:
            self.q2.put(self.q1.get())
        ele = self.q1.get()
        while not self.q2.empty():
            self.q1.put(self.q2.get())
        return ele
    
    def top(self):
        if self.q1.empty():
            return -1
        while self.q1.qsize() != 1:
            self.q2.put(self.q1.get())
        ele = self.q1.get()
        while not self.q2.empty():
            self.q1.put(self.q2.get())
        self.q1.put(ele)
        return ele
        
           
    def getSize(self):
        return self.q1.qsize()
        
    
s = StackUsingQueues()
li = [int(ele) for ele in input().split()]
i=0
while i<len(li):
    choice = li[i]
    if choice == -1:
        break
    elif choice == 1:
        s.push(li[i+1])
        i+=1
    elif choice == 2:
        ans = s.pop()
        if ans!=0:
            print(ans)
        else:
            print(-1)
    elif choice == 3:
        ans = s.top()
        if ans!=0:
            print(ans)
        else:
            print(-1)
    elif choice == 4:
        print(s.getSize())
    elif choice == 5:
        while s.q1.qsize() !=0:
            print(s.q1.get(),end=' ')
            
    i+=1