Oo, or even
: triples ( n -- seq )
iota rest 3 [ first3 triple? ] filter-combinations ;
On Mon, May 20, 2013 at 7:06 PM, Alex Vondrak <ajvond...@gmail.com> wrote:
> Or, going by the algorithms in the wiki:
>
> ```
> USING: arrays kernel locals math math.ranges sequences
> sequences.extras ;
>
> :: triples ( n -- seq )
> n [1,b] [| x |
> x n [a,b] [| y |
> y n [a,b]
> [| z | x sq y sq + z sq = ]
> [| z | x y z 3array ]
> filter-map
> ] map concat
> ] map concat ;
> ```
>
> Fun bug report: using `map-concat` from `sequences.extras` fails to
> compile for me---complains about using `call` on a run-time computed value.
>
> But, I really like your approach using `all-combinations`. It yields a
> much nicer-looking version:
>
> ```
> : triple? ( x y z -- ? )
> [ sq ] tri@ [ + ] dip = ;
>
> : triples ( n -- seq )
> iota rest 3 all-combinations [ first3 triple? ] filter ;
> ```
>
> Regards,
> --Alex Vondrak
>
>
>
> On Mon, May 20, 2013 at 8:18 AM, _ _ <wzr...@gmail.com> wrote:
>
>> ! Copyright (C) 2013 Your name.
>> ! See http://factorcode.org/license.txt for BSD license.
>> USING: kernel sequences math math.functions arrays math.combinatorics ;
>> IN: pythagorean-triples
>>
>> : a-b-list ( n -- seq )
>> iota rest 2 all-combinations ;
>>
>> : a-b-c ( seq1 -- seq2 )
>> [ first ]
>> [ second ]
>> [ [ first sq ] [ second sq ] bi + sqrt ]
>> tri
>> 3array ;
>>
>> : a-b-c-list ( n -- seq )
>> a-b-list [ a-b-c ] map ;
>>
>> : float.0? ( n -- ? )
>> dup floor 0 ~ ;
>>
>> : (pythagoreans) ( n -- seq )
>> a-b-c-list [ third float.0? ] filter ;
>>
>> : pythagoreans ( n -- seq )
>> (pythagoreans) [ [ first ] [ second ] [ third >integer ] tri 3array ]
>> map ;
>>
>>
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>
>
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