What would be the best way to implement the Fannkuch benchmark in J?
>From the shootout page (http://tinyurl.com/f3wdz):
a) Take a permutation of {1,...,n}, for example: {4,2,1,5,3}.
b) Take the first element, here 4, and reverse the order of the first
4 elements: {5,1,2,4,3}.
c) Repeat this until the first element is a 1, so flipping won't
change anything more: {3,4,2,1,5}, {2,4,3,1,5}, {4,2,3,1,5},
{1,3,2,4,5}.
d) Count the number of flips, here 5.
e) Do this for all n! permutations, and record the maximum number of
flips needed for any permutation.
I came with the following immediate solution:
a) and b)
---------
fn =: {. (([EMAIL PROTECTED]@[ { ]) , }.) ]
fn 4 2 1 5 3
5 1 2 4 3
c) and d)
---------
c =: (>:@$:@fn)`0:@.({.=1:)"1
c 4 2 1 5 3
5
e)
--
m =: >./@:c@([EMAIL PROTECTED] A. >:@i.)
m 5
7
However, "m 10" takes ages to compute compared to what is done in
other languages. What would be the best way to code this benchmark?
I'm surprised not to see J entries in the Shootout benchmark. J would
rock in terms of number of lines :)
Sam
--
Samuel Tardieu -- [EMAIL PROTECTED] -- http://www.rfc1149.net/
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