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StackusingQueue.py

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# 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