sudoku in J (translation of APL algorithm)

sudoku.ijs

s44 =: 4 4 $ 0 0 0 0 0 0 2 1 3 0 0 4 0 0 0 0

box =: (] #"1 ] # ([: i. 2 # ]))

indices =: 3 : 0
 yy =. {. y
 a =. yy #"0 i. yy
 b =. |: a
 c =. a ,/"0 b
)

rcb =: 3 : 0
 yy =. {. y
 c =. indices y
 rcb =. c ,/"(1 0) (box %: yy)
)

NB. <"1 (rcb 4 4)

cmap =: 1 e."1 (] ="(1 1)/ ])

NB. <"2 cmap rcb $ s44

avl =: 4 : '((1+i.{.$y) -. y * (<x) { cmap rcb $ y)'
NB.(tacit:) avl =: (1+[:i.[:{.[:$]) -. ] * ([:<[) { [: cmap [: rcb [: $ ]
NB. 2 1 avl s44

pvec =: 4 : 0
 <"2 (x avl y) (<x) }/"(0 2) y
)
NB. 0 0 pvec s44

pvex =: [: ; [ ([: < pvec)"1 2 [: > ]

NB. 1 0 pvex 1 1 pvex 0 0 pvex s44

emt =: 3 : 0
 a =. , ;/"2 indices $ y
 b =. , 0 = s44
 b # a
)

svec =: 3 : 'pvex&:>/ (emt y), <y'
svec s44