155.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-


__author__ = ['"wuyadong" <wuyadong311521@gmail.com>']


class MinStack(object):

    def __init__(self):
        """
        initialize your data structure here.
        """
        self.stack = []
        self.min_num = None

    def push(self, x):
        """
        :type x: int
        :rtype: void
        """
        self.stack.append(x)
        if self.min_num is not None and self.min_num > x:
            self.min_num = None

    def pop(self):
        """
        :rtype: void
        """
        pop_num = self.stack.pop()
        if self.min_num is not None and pop_num == self.min_num:
            self.min_num = None

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

    def getMin(self):
        """
        :rtype: int
        """
        if self.min_num is None:
            self.min_num = min(self.stack)

        return self.min_num


# 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()