#=====================================================================
# Author: Isai Damier
# Title: Stack With Get-Min
# Project: geekviewpoint
# Package: datastructure
#
# Description: Normally, only the top of a stack is available for
# peeking and popping. Here, however, the requirement is to make
# the minimum value on the stack always viewable in O(1).
# To that end, in addition to the primary stack of operation
# (called primary), a separate stack (called minimums) must be
# used to track the minimum value on the primary stack. The point
# is not to pop the minimum value in O(1) that would require a
# bit more work. Rather, the getMinimum function allows peeking
# into the stack, as it were, to see the minimum value on the
# stack.
#
# Throughout the implementation it should be clear that the
# primary stack is the real (i.e. representative) stack and that
# the minimums stack is an auxiliary stack that exists only so
# the getMinimum() function may exist.
#=====================================================================
from Queue import LifoQueue
class StackWithGetMin( object ):
def __init__( self ):
self.primary = LifoQueue()
self.minimums = LifoQueue()
#=====================================================================
# Statement:
# Indicate the minimum value on the stack.
#
# Time Complexity of Solution:
# Best = Average = Worst = const.
#
# Technical Details: This one-line function is the reason for this
# whole datastructure. Notice how the minimums stack is not
# maintained here. minimums is maintained by the push and the
# pop functions. The only operation in getMinimum is peeking
# into the minimums stack. Nonetheless, the minimums stack
# exists entirely for this function.
#
#=====================================================================
def getMinimum( self ):
return self.minimums.queue[self.minimums.qsize() - 1]
import unittest
from algorithms.StackWithGetMin import StackWithGetMin
class StackWithGetMinTest( unittest.TestCase ):
#=====================================================================
# Test of getMinimum method, of class StackWithGetMin.
#=====================================================================
def testGetMinimum( self ):
stack = StackWithGetMin()
self.assertTrue( stack.isEmpty() )
self.assertEquals( 0, stack.size() )
inputs = [40, 65, 5, 6, 32, 4, 7, 1, 2, 84, 9, 10]
for i in inputs:
stack.push( i )
self.assertFalse( stack.isEmpty() )
self.assertEquals( len( inputs ), stack.size() )
mins = [40, 5, 4, 1]
min = len( mins ) - 1
for i in range( len( inputs ) - 1, -1, -1 ):
self.assertEquals( inputs[i], stack.pop() )
if not stack.isEmpty():
if stack.getMinimum() != mins[min]:
min -= 1
self.assertEquals( mins[min], stack.getMinimum() )
self.assertTrue( stack.isEmpty() )
self.assertEquals( 0, stack.size() )
