! http://phildawes.net/blog/2009/03/30/factor-makes-you-write-better-code/

IN: sma

USING: kernel sequences math arrays math.ranges math.order ;

: partial-sums ( seq -- newseq )
    0 [ + ] accumulate
    swap suffix 1 tail ;

: differences ( seq seq -- newseq )
    [ - ] 2map ;

: prepad ( seq n elt -- newseq )
    <array> prepend ;
    
: sliding-partial-sums ( seq n -- newseq )
    dupd 0 prepad differences partial-sums ;
    
: plateau ( len n -- seq )
    [ min [1,b] ]
    [ - 0 max ]
    [ nip <array> ] 2tri append ;
    
: sma ( seq n -- newseq )
    [ sliding-partial-sums ]
    [ [ length ] dip plateau ] 2bi
    [ / ] 2map ;