1. class MinStack(object):
    3.     def __init__(self):
    4.         """
    5.         initialize your data structure here.
    6.         """
    7.         self.stack = []
    8.         self.min_stack = []
    11.     def push(self, x):
    12.         """
    13.         :type x: int
    14.         :rtype: None
    15.         """
    16.         self.stack.append(x)
    17.         if self.min_stack == []:
    18.             self.min_stack.append(x)
    19.         else:
    20.             val = min(x, self.min_stack[-1])
    21.             self.min_stack.append(val)
    25.     def pop(self):
    26.         """
    27.         :rtype: None
    28.         """
    29.         self.stack.pop(-1)
    30.         self.min_stack.pop(-1)
    33.     def top(self):
    34.         """
    35.         :rtype: int
    36.         """
    37.         return self.stack[-1]
    40.     def min(self):
    41.         """
    42.         :rtype: int
    43.         """
    44.         return self.min_stack[-1]
    48. # Your MinStack object will be instantiated and called as such:
    49. # obj = MinStack()
    50. # obj.push(x)
    51. # obj.pop()
    52. # param_3 = obj.top()
    53. # param_4 = obj.min()