Well hello there, come to play the famous Diamond Game?

The rules are notoriously simple. Here's an ace of diamonds card (it's larger than normal), and here are a pile of pennies. We each take turns to place pennies on the card. Whoever is first not to be able to fit a penny onto the card loses.

Tell you what, you go first this time. Put a tenner on it. If you win, you'll get twenty!

How can the player guarantee that they win every time, regardless of how the barkeep plays?

For the purposes of the game, assume that both players are able to exactly follow any rule or process, regardless of its complexity.


Actually, I heard about this puzzle and resolved it once, so it's easy for me, sorry.

To ensure, that you'll win,

you must start at the very center of the card. The other player will put a coin at a random position. You just have to put yours symmetrically to the other's, with the center of your first. Since, there will be for every opponent coin a symmetrical place, you will win with this method.

  • $\begingroup$ It's always funny to see people try this in go. They get rekt $\endgroup$ – Jacob Goulden May 30 '16 at 18:45
  • $\begingroup$ @JacobGoulden Look, if somebody will put an another answer, I will upvote it. If this answering method is not suitable for Puzzle SE, then okay, I learned from this. $\endgroup$ – Lasoloz May 30 '16 at 18:48
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    $\begingroup$ @Lasoloz I think it is perfect for Puzzle SE $\endgroup$ – Fabich May 30 '16 at 19:29
  • $\begingroup$ @Lordofdark Okay, thank you. I actually added the resolved part, because first I did not think that my words imply that I just copy-pasted. Unfortunately I'm not native English speaker. $\endgroup$ – Lasoloz May 30 '16 at 19:39

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