Monday math: Game time!

by rrusczyk, May 9, 2011, 4:51 PM

So you want to play a game? How about Wythoff's game?

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This game was featured on the USACO US OPEN this year.

by fortenforge, May 9, 2011, 5:46 PM

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Seems like an interesting article, though I didn't follow all the details. I don't think it mentioned the beautiful connection to http://en.wikipedia.org/wiki/Beatty_sequence (but the example on that wikipedia page does allude to Wythoff's game)

by joshuazucker, May 9, 2011, 6:26 PM

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There's an interesting connection between Wythoff's game and this year's USAJMO, #4. In the problem, we define a sequence of words $W_n$. Here are the first few words $W_n$ and $S_n$, where $S_n$ is $W_n$ written backwards:
\[
\begin{array}{c|l|l}
n & W_n & S_n \\ \hline
0 & a & a \\
1 & b & b \\
2 & ab & ba \\
3 & bab & bab \\
4 & abbab & babba \\
5 & bababbab & babbabab \\
6 & abbabbababbab & babbababbabba
\end{array}
\]

Every word $S_n$ is the first part of the next word $S_{n + 1}$, so each word $S_n$ can be considered the first part of an infinitely long word $S$. The question is, for a positive integer $k$, how can you tell if the $k$th letter in $S$ is $a$ or $b$?

by nsato, May 9, 2011, 11:47 PM

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AMAZING GAME!! SOO COOL. Analyzing this, here is what I have so far:
In these situations this is what will happen, given both players make their best moves:
x and x: Won game; just take everything.
x and x+1: Won game; leave 2 on one side, 1 on the other. Note that the exception to this is 1 and 2.
x and x+2: Still working on it...

by Lalagato, Jun 6, 2011, 1:51 AM

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