The game itself is played by initially dealing players a hand of 4 cards. You are right that it shouldn't be a constraint, but I guess for the sake of the game rules, I actually specified "A hand of four cards" in the description (Input). Although it is quite vague, I should have mentioned it more explicitly.

good point, thank you for the feedback!

super fun! what a nice warm-up to algorithms.

i mean, it's a relatively fast solution

still can't get over how smart this solution is

Hmmm, I'm not sure because the suits don't really come in order, like there is no suit that is higher than another.

Resolved. Thank you!

I have updated the test cases to include various fixed tests. Thank you for your suggestions and feedback, I will be sure to use them for my next katas.

You're right. I will update the kata soon. Thank you for the suggestion.

For ISBN-10 validation, the rightmost number is the first position, not the leftmost.