Usernames is a nice example. Just as a demo, we could make things simpler: Look at all the usernames in the input, keep track of all the letters you’ve seen. W

Usernames is a nice example. Just as a demo, we could make things simpler: Look at all the usernames in the input, keep track of all the letters you’ve seen. When you get a new name, if you’ve seen all the letters before, you might have seen the name before. If there’s a new letter, it must be a new name. Obviously that isn’t a great hash function, some letters are more common than others, so real Bloom filters use better ones, but it works basically the same way.