#=====================================================================
# Author: Isai Damier
# Title: QueueWithStack
# Project: geekviewpoint
# Package: datastructure
#
# Description: To implement a Queue using Stack datastructure,
# two stacks are sufficient: a stack for enqueuing and a stack
# for dequeuing. Recall that stacks are LIFO objects (i.e. Last
# In First Out), whereas queues are normally FIFO objects (i.e.
# First In First Out). Hence although adding elements to a stack
# is similar to adding elements to a queue, the removal process
# for each datastructure is different.
#
# Notice how in the following implementation queue.enqueue() is
# the same as stack.put(). However, two stacks are used for
# proper dequeuing.
#=====================================================================
from Queue import LifoQueue
class QueueWithStack( object ):
def __init__( self ):
self.input_stack = LifoQueue()
self.output_stack = LifoQueue()
#=====================================================================
# Statement:
# Indicate whether the queue is empty.
#
# Time Complexity of Solution:
# Best = Average = Worst = const.
#
# Technical Details: The queue is empty precisely when both the
# input_stack stack and the output_stack stack are empty.
#
# Note that the input_stack stack may occasionally be empty
# while the output_stack stack is not empty vice versa.
#
#=====================================================================
def isEmpty( self ):
return self.input_stack.empty() and self.output_stack.empty()
import unittest
from algorithms.QueueWithStack import QueueWithStack
class Test( unittest.TestCase ):
#=====================================================================
# Test of isEmpty method, of class QueueWithStack.
#=====================================================================
def testIsEmpty( self ):
queue = QueueWithStack()
data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
self.assertTrue( queue.isEmpty() )
self.assertEquals( 0, queue.size() )
for d in data:
queue.enqueue( d )
self.assertFalse( queue.isEmpty() )
self.assertEquals( len( data ), queue.size() )
