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math.combinatorics: use nth-unsafe more.

db4
John Benediktsson 2013-04-06 12:43:02 -07:00
parent d15dbaebb4
commit 64111e1342
1 changed files with 6 additions and 3 deletions
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basis/math/combinatorics/combinatorics.factor
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@ -49,10 +49,13 @@ MEMO: factorial ( n -- n! )
: permutation-iota ( seq -- iota )
length factorial iota ; inline
: nths-unsafe ( indices seq -- seq' )
[ [ nth-unsafe ] curry ] keep map-as ;
PRIVATE>
: permutation ( n seq -- seq' )
[ permutation-indices ] keep nths ;
[ permutation-indices ] keep nths-unsafe ;
TUPLE: permutations length seq ;
@ -139,13 +142,13 @@ PRIVATE>
:: combinations-quot ( seq k quot -- seq quot )
seq length :> n
n k nCk iota [
k n combination-indices seq nths quot call
k n combination-indices seq nths-unsafe quot call
] ; inline
PRIVATE>
: combination ( m seq k -- seq' )
swap [ length combination-indices ] [ nths ] bi ;
swap [ length combination-indices ] [ nths-unsafe ] bi ;
TUPLE: combinations seq k length ;