1. Code

class MyHashSet:
    def __init__(self):
        self.my_hash = {}

    def add(self, key: int) -> None:
        self.my_hash[key] = "dummy"

    def remove(self, key: int) -> None:
        if key in self.my_hash:
            del self.my_hash[key]

    def contains(self, key: int) -> bool:
        if key in self.my_hash:
            return True
        else:
            return False

2. Result

        Runtime : 136 ms(98.60%), Memory usage : 19 MB(54.50%)
        (Runtime can be different by a system even if it is a same code.)

Check out the my GitHub repo for more info on the code. If you have questions, you can leave a reply on this post.