155_Min_Stack.py

# class MinStack(object):
#     def __init__(self):
#         """
#         initialize your data structure here.
#         """
#         self.stack = []
#         self.min_stack = []


#     def push(self, x):
#         """
#         :type x: int
#         :rtype: nothing
#         """
#         self.stack.append(x)
#         if len(self.min_stack) == 0 or x <= self.min_stack[-1]:
#             self.min_stack.append(x)


#     def pop(self):
#         """
#         :rtype: nothing
#         """
#         if len(self.stack) > 0:
#             last = self.stack[-1]
#             # Need to check whether pop minStack
#             if len(self.min_stack) > 0 and last == self.min_stack[-1]:
#                 self.min_stack.pop()
#             self.stack.pop()


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


#     def getMin(self):
#         """
#         :rtype: int
#         """
#         if len(self.min_stack) > 0:
#             return self.min_stack[-1]
#         else:
#             if len(self.stack) > 0:
#                 return self.stack[-1]
#             return None

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


    def push(self, x):
        """
        :type x: int
        :rtype: nothing
        """
        self.stack.append(x)
        if len(self.min_stack) == 0:
            self.min_stack.append(x)
            return
        if x <= self.min_stack[-1]:
            self.min_stack.append(x)
        else:
            # Push top of min stack again
            self.min_stack.append(self.min_stack[-1])


    def pop(self):
        """
        :rtype: nothing
        """
        if len(self.stack) > 0:
            # Much simple than solution 1
            # But use more space
            self.min_stack.pop()
            self.stack.pop()


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


    def getMin(self):
        """
        :rtype: int
        """
        if len(self.min_stack) > 0:
            return self.min_stack[-1]
        return None