(This article was originally published at Xi'an's Og » R, and syndicated at StatsBlogs.)
The little half puzzle proposed a “dumb’ solution in that players play a minimax strategy. There are 34 starting values less than 100 guaranteeing a sure win to dumb players. If instead the players maximise their choice at each step, the R code looks like this:
solveO=function(n){
if (n<3){ solve=(n==2)}else{
solve=(!(solveO(n-1)))||(!solveO(ceiling(n/2)))}
solve}
and there are now 66 (=100-34, indeed!) starting values for which the starting player can win.
Incidentally, I typed
> solveO(1113) Error: evaluation nested too deeply: infinite recursion / options(expressions=)?
which shows R cannot handle heavy recursion without further programming. Testing for the upper limit, I found that the largest acceptable value is 555 (which takes forever to return a value, predicted at more than one hour by a linear regression on the run times till 300…).
Filed under: R, Statistics Tagged: Le Monde, mathematical puzzle, R, recursion
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