以查找最小值为例

class MyStack:
    def __init__(self):
        self.values = []
        self.mins = []

    def push(self, ins):
        if not self.mins:
            self.mins.append((0, ins))
        elif ins < self.mins[-1][1]:
            self.mins.append(
                (len(self.values), ins)
            )
        self.values.append(ins)

    def pop(self):
        if self.mins and len(self.values)-1 == self.mins[-1][0]:
            self.mins.pop()
        return self.values.pop() if self.values else None

    # def top(self):
    #     return self.values[-1] if self.values else None

    def get_min(self):
        return self.mins[-1][1] if self.mins else None