Problem#155 Min Stack

Problem

Solution

# 法一：差值法
class MinStack:

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


    def push(self, x: int) -> None:
        self.stack.append(x - self.min_v)
        if x < self.min_v:
            self.min_v = x


    def pop(self) -> None:
        if self.stack[-1] < 0:
            last_min = self.min_v - self.stack[-1]
            self.min_v = last_min
            self.stack.pop()
        else:
            self.stack.pop()


    def top(self) -> int:
        if self.stack[-1] < 0:
            return self.min_v
        else:
            return self.stack[-1] + self.min_v

    def getMin(self) -> int:
        return self.min_v



# 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()

# 法二：雙棧法
class MinStack:

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


    def push(self, x: int) -> None:
       self.stack.append(x)
       if len(self.min_stack) == 0 or x <= self.min_stack[-1]:
           self.min_stack.append(x)


    def pop(self) -> None:
        temp = self.stack.pop()
        if temp == self.min_stack[-1]:
            self.min_stack.pop()


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


    def getMin(self) -> int:
        return self.min_stack[-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()