Gin Rummy — free card game against the computer

Ten cards each. On your turn you take one card — from the face-down stock or the face-up discard — and throw one away. You are trying to arrange your hand into sets (three or four of the same rank) and runs (three or more in sequence in one suit), leaving as little as possible unmatched.

Those unmatched cards are your deadwood. Get them to ten points or less and you may knock, which ends the hand and compares the two hands. One deal per round, and your score is rounds won in a row. Free, no download, no sign-up, and a half-finished hand is saved if you close the tab.

How to play

• Take the stock or the discard, then tap a card in your hand twice to throw it away.
• Green cards are in a meld. The deadwood number in the header counts only the rest.
• Knock at ten or less. The button lights up when you legally can, and it throws your worst card for you. Knocking at zero is gin and pays a bonus.
• Watch the discard pile. Anything you take from it, the computer has seen, and it plays accordingly.
• If the stock runs down to two cards with no knock, the hand is a draw — and a draw ends your run, like a loss.

The card that can be in two melds, and why that is the whole problem

Finding melds in a hand looks like an easy job until you meet the case that makes it hard. Hold the 7, 8 and 9 of hearts and the 7 of clubs, 7 of spades and 7 of diamonds and you have a run and a set — but the seven of hearts can only be in one of them. Every serious rummy hand contains a version of that question, and answering it wrong costs you real points.

This is why the deadwood number under your hand is worth trusting. It is not a guess or a greedy scan: every possible meld in your hand is enumerated, and then the best combination of non-overlapping melds is searched for exactly. When two melds compete for a card, the arrangement that leaves the least deadwood wins, and that is the one shown in green.

The second thing worth knowing is when to knock. Knocking is not free: you win only if your deadwood is lower than your opponent's after they lay off any cards that extend your melds. If they equal or beat you, that is an undercut and they take the difference plus a bonus, which is where the usual advice comes from — hold on, keep improving, and knock on something better than ten.

That advice does not survive measurement here. Two identical players were run against this opponent for a few hundred rounds each, one knocking at the first legal moment and one holding out for a hand of four or less: they finished within five points of each other, both a shade under half the rounds. Waiting is not free either. Every turn you spend improving is a turn the opponent might knock first, and the hands you lose that way cancel out the undercuts you avoided. So knock when you can, and treat the wait as a real cost rather than as patience.

The third is that the discard pile is public information and it runs both ways. When you take a card from it, everyone knows what you took, and a careful opponent stops feeding that suit or rank. The computer here does exactly that, and nothing more — it reads the discards it has seen and never looks at your hand, which is the same rule the Hearts and Dominoes opponents on this site follow. An opponent that peeks is not harder, it is broken.

More games

More from 🃏 Card & solitaire games:

• Yukon Solitaire — Klondike with no deck to draw from. Any card moves, and its whole pile comes along.
• Cribbage — Throw two to your crib, peg to thirty-one, then count the show. One deal at a time.
• Speed — No turns at all. Both of you play at once, one rank up or down, until someone runs out.
• Solitaire — Classic Klondike, built for one hand: tap a card and it moves itself. Undo, auto-finish, and your best time saved.
• FreeCell — Every card face up from the start, so there's no luck left to blame. Four free cells and a clock.

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