StackusingQueue.py

# Program to implement a stack using 
# two queue 
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()) 

# This code is contributed by PranchalK