answer.py

#!/usr/bin/env python3

#-------------------------------------------------------------------------------
class MinStack(object):

    def __init__(self):
        """
        initialize your data structure here.
        """
        self.stack = []
        

    def push(self, x):
        """
        :type x: int
        :rtype: void
        """
        # Keep track of min
        if not self.stack:
            self.stack.append((x, x))
        else:
            self.stack.append((x, min(x, self.stack[-1][1])))
        

    def pop(self):
        """
        :rtype: void
        """
        if self.stack:
            self.stack.pop()
        

    def top(self):
        """
        :rtype: int
        """
        if self.stack:
            return self.stack[-1][0]
        else:
            return None
        

    def getMin(self):
        """
        :rtype: int
        """
        if self.stack:
            return self.stack[-1][1]
        else:
            return None
        
#-------------------------------------------------------------------------------