combination-indices ( x! p n -- seq )

Vocabulary

math.combinatorics.private

Inputs

x!	an object
p	an object
n	an object

Outputs

seq

an object

Definition

USING: arrays kernel math math.combinatorics sequences
sequences.private ;

IN: math.combinatorics.private

:: combination-indices ( x! p n -- seq )
    x 1 + x! p 0 <array> :> c 0 :> k! 0 :> r! p 1 - [| i |
        i [ 0 ] [ 1 - c nth-unsafe ] if-zero i c set-nth-unsafe
        [ k x < ] [
            i c [ 1 + ] change-nth-unsafe n i c nth-unsafe -
            p i 1 + - nCk r! k r + k!
        ] do while k r - k!
    ] each-integer p 2 < [ 0 ] [ p 2 - c nth-unsafe ] if p 1 <
    [ drop ] [ x + k - p 1 - c set-nth-unsafe ] if c
    [ 1 - ] map! ;