2 USING: arrays kernel sequences errors namespaces math ;
4 : <range> ( from to -- seq ) dup <slice> ; inline
5 : (0..n] ( n -- (0..n] ) 1+ 1 swap <range> ; inline
6 : [1..n] ( n -- [1..n] ) (0..n] ; inline
7 : [k..n] ( k n -- [k..n] ) 1+ <range> ; inline
8 : (k..n] ( k n -- (k..n] ) [ 1+ ] 2apply <range> ; inline
10 : Z:(-inf,0]? ( n -- bool )
11 #! nonpositive integer
12 dup 0 <= [ integer? ] [ drop f ] if ;
14 : factorial ( n -- n! ) (0..n] product ;
16 : factorial-part ( k! k n -- n! )
17 #! calculate n! given n, k, k!
21 #! uses the results from min(k!,(n-k)!) to compute max(k!,(n-k)!)
22 #! use max(k!,(n-k)!) to compute n!
26 [ - ] 2keep rot 2dup < [ swap ] when
27 [ factorial ] keep over
28 >r rot [ factorial-part ] keep rot pick >r factorial-part r> r> * /
32 #! uses the results from (n-k)! to compute n!
36 2dup - nip [ factorial ] keep rot pick >r factorial-part r> /
39 : inverse-permutation ( seq -- seq )
40 dup length dup 0 <array> -rot swap [ pick set-nth ] 2each ;