min_stack.py

class MinStack(object):

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

    def push(self, x):
        """
        :type x: int
        :rtype: void
        """
        self.stack.append(x)
        if len(self.mini) == 0  or x <= self.mini[-1]:
            self.mini.append(x)

    def pop(self):
        """
        :rtype: void
        """
        num = self.stack.pop()
        if num == self.mini[-1]:
            self.mini.pop()

    def top(self):
        """
        :rtype: int
        """
        return self.stack[-1]


    def getMin(self):
        """
        :rtype: int
        """
        return self.mini[-1]



# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(x)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()