剑指 Offer 30. 包含min函数的栈

solution

1. naive

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 not self.min_stack or x <= self.min_stack[-1]:
            self.min_stack.append(x)
        else:
            self.min_stack.append(self.min_stack[-1])

    def pop(self) -> None:
        self.min_stack.pop()
        self.stack.pop()

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


    def min(self) -> int:
        return self.min_stack[-1]

2. space save

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 not self.min_stack or x <= self.min_stack[-1]:
            self.min_stack.append(x)

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

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


    def min(self) -> int:
        return self.min_stack[-1]