LeetCode 155 – Python 3 (Week 3 – 04)

class MinStack:

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

    def push(self, x: int) -> None:
        cur_min = self.getMin()
        if cur_min == None or x < cur_min: cur_min = x #here we can not use if not cur_min. Because if cur_min is 0, it will be considered as not cur_min is true! 
        self.array.append((x, cur_min))
        

    def pop(self) -> None:
        self.array.pop()
        

    def top(self) -> int:
        if not self.array: return None
        return self.array[-1][0]
        

    def getMin(self) -> int:
        if not self.array: return None
        return self.array[-1][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()