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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