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math.combinatorics: speed up selections word.

factor-shell
John Benediktsson 2018-01-17 10:36:12 -08:00
parent 9a4441a80e
commit 3bf23d242d
1 changed files with 16 additions and 6 deletions
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basis/math/combinatorics/combinatorics.factor
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@ -3,8 +3,8 @@
USING: accessors arrays assocs binary-search classes.tuple USING: accessors arrays assocs binary-search classes.tuple
combinators fry hints kernel kernel.private locals math combinators fry hints kernel kernel.private locals math
math.order math.ranges namespaces sequences sequences.private math.functions math.order math.ranges namespaces sequences
sorting strings vectors ; sequences.private sorting strings vectors ;
IN: math.combinatorics IN: math.combinatorics
<PRIVATE <PRIVATE
@ -251,10 +251,20 @@ PRIVATE>
<PRIVATE <PRIVATE
: (selections) ( seq n -- selections ) :: next-selection ( seq n -- )
[ dup [ 1sequence ] curry { } map-as dup ] [ 1 - ] bi* [ 1 seq length 1 - [
cartesian-product concat [ concat ] map over 0 =
] with times ; ] [
[ seq [ + n /mod ] change-nth-unsafe ] keep
] do until 2drop ; inline
:: (selections) ( seq n -- selections )
seq length :> len
n 0 <array> :> idx
len n ^ [
idx seq nths-unsafe
idx len next-selection
] replicate ;
PRIVATE> PRIVATE>