Gin Rummy

Draw, discard, knock · two players, to 100

Stock

Discard

Your hand

Dealing…

Hand 1

First to 100 points wins the game, with 25 for every hand won and 100 for the game itself.

Table

This hand

Game

Play against

Strength

Loose cards

Group my sets and runs for me

How to play

Ten cards each. On your turn take a card — the face-up discard or the top of the stock — and then throw one away, so you always end with ten.
Build sets (three or four of a kind) and runs (three or more in a row in one suit; the ace is low, and the run doesn't turn the corner at the king).
Everything outside a set or a run is deadwood. Aces count 1, court cards 10, everything else its own number.
Knock when the card you throw away leaves you ten points of deadwood or less. Your opponent then lays any of their loose cards onto your sets and runs, and you score the difference between the two piles of deadwood.
Lay every card down and it's gin: nothing can be laid off against you, and you take the other hand's deadwood plus 25.
Knock and come off worse and you have been undercut: your opponent takes the difference plus 25.
The first play of a hand is the turned-up card: it's offered to the player who wasn't dealing, then to the dealer, and if neither wants it the first draw comes off the stock.
You can't throw back the very card you just took from the discard pile, and when the stock is down to its last two cards the hand is dead — nobody scores and it's dealt again.
Play runs to 100. The winner adds 100 for the game and 25 for every hand they won, and doubles the lot if their opponent never scored.
How the computer plays: it sees its own ten cards, the discard pile and what you have taken from it — nothing else. It works out the best way to lay its hand down and weighs how close each loose card is to joining something. Hard also remembers every card you have taken and every card you have thrown, holds back the ranks and suits you look like you are collecting, and takes a knock as soon as one is there; Normal plays its own hand and waits for a tidier knock; Easy throws whatever costs it most and knocks at the first chance.
Online friend sends a link. The deck is shuffled by both devices together — each adds a secret number, sealed with a cryptographic hash before the other's is seen — and at the end of every hand your device checks the whole deck against that promise.
Hint shows what the strongest computer would do. Press F for a full-screen table.

Knock	the difference in deadwood
Gin	their deadwood + 25
Undercut	the difference + 25
Every hand won	25 at the end
Winning the game	100, doubled in a shutout