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Push

#===================================================================== # 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: # Add the given element to the stack. # # Time Complexity of Solution: # Best = Average = Worst = const. # # Technical Details: If the stack is empty, then the given element # is perforce also the minimum element on the stack. Therefore # mark the element as minimum by also pushing it into the # minimums stack. On the other hand, if the stack (i.e. the # primary stack) is not empty, check if the new element is less # than the current minimum element. If it is, make the new # element the new minimum. # # The explanation is slightly different from the actual code # to give the reader a different viewpoint. # #===================================================================== def push( self, e ): if self.primary.empty() or e < self.minimums.queue[self.minimums.qsize() - 1]: self.minimums.put( e ) self.primary.put( e )

import unittest from algorithms.StackWithGetMin import StackWithGetMin class StackWithGetMinTest( unittest.TestCase ): #===================================================================== # Test of push method, of class StackWithGetMin. #===================================================================== def testPush( self ): e = 0 stack = StackWithGetMin() 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() )