cc 3.2

stackMin.py

#3.2  How would you design a stack which, in addition to push and pop, also has a function min which returns the minimum element? Push, pop and min should all operate in O(1) time.

from stack import Stack, Node

class stackmin(Stack):

    def __init__(self):
        Stack.__init__(self)
        self.min = Stack()
        self.minItem = None

    def push(self, item):
        Stack.push(self,item)
        if self.minItem is not None: 
            if self.minItem < item:
                self.minItem = item
        else:
            self.minItem = item
        self.min.push(self.minItem)

    def pop(self):
        Stack.pop(self)
        self.min.pop() 
          
    def printStack(self):
        Stack.printStack(self)
    
    def stackMin(self):
        print 'the min:', self.min.top.item    
    
#test
stack = stackmin()
stack.push(1)
stack.push(2)
stack.push(3)
stack.push(4)
stack.stackMin()
stack.pop()
stack.stackMin()