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(use-modules
(srfi srfi-1)
(srfi srfi-26)
(ice-9 match)
(ice-9 textual-ports)
(sat solver)
(sat helpers))
(define (get-value board vals col row)
(1+
(find
(lambda (possible-value)
(array-ref vals
(array-ref board col row possible-value)))
(iota 9))))
(define (set-initial-value board col row val)
(add-clause
(list
(array-ref board
col
row
(1- val)))))
(define (make-row row)
(map
(cut cons <> row)
(iota 9)))
(define (make-col col)
(map
(cut cons col <>)
(iota 9)))
(define (rows)
(map
(cut make-row <>)
(iota 9)))
(define (cols)
(map
(cut make-col <>)
(iota 9)))
(define (make-box bcol brow)
(let ((l '()))
(do ((icol 0 (1+ icol))) ((= icol 3))
(do ((irow 0 (1+ irow))) ((= irow 3))
(set! l (cons
(cons (+ (* 3 bcol) icol)
(+ (* 3 brow) irow))
l))))
l))
(define (boxes)
(let ((l '()))
(do ((bcol 0 (1+ bcol))) ((= bcol 3))
(do ((brow 0 (1+ brow))) ((= brow 3))
(set! l (cons
(make-box bcol brow)
l))
))
l))
(define (unique-values board coords-list)
(for-each
(lambda (n)
(exactly-one-true
(map
(lambda (coord)
(array-ref board (car coord) (cdr coord) n))
coords-list)))
(iota 9)))
(define (all-unique-values board coord-lists)
(for-each
(cut unique-values board <>)
coord-lists))
(define (make-board)
(let ((board (make-array #f 9 9 9)))
(array-map! board make-sat-variable)
board))
(define (exactly-one-number board col row)
(exactly-one-true
(map
(lambda (value)
(array-ref board col row value))
(iota 9))))
(define (char->number c)
(match c
(#\0 0)
(#\1 1)
(#\2 2)
(#\3 3)
(#\4 4)
(#\5 5)
(#\6 6)
(#\7 7)
(#\8 8)
(#\9 9)))
(define (process-line board row line)
(map
(lambda (c col)
(when (char-numeric? c)
(set-initial-value
board
col
row
(char->number c))))
(string->list line)
'(0 1 2 _ 3 4 5 _ 6 7 8)))
(define (read-sudoku port board)
(process-line board 0 (get-line port))
(process-line board 1 (get-line port))
(process-line board 2 (get-line port))
(get-line port)
(process-line board 3 (get-line port))
(process-line board 4 (get-line port))
(process-line board 5 (get-line port))
(get-line port)
(process-line board 6 (get-line port))
(process-line board 7 (get-line port))
(process-line board 8 (get-line port)))
(define (print-sudoku board vals)
(do ((row 0 (1+ row))) ((= row 9))
(do ((col 0 (1+ col))) ((= col 9))
(format #t "~a" (get-value board vals col row))
(when (or (= col 2)
(= col 5))
(display "|")))
(newline)
(when (or (= row 2)
(= row 5))
(display "-----------\n"))))
(let ((board (make-board)))
;; Each position contains exactly one number
(do ((col 0 (1+ col))) ((= col 9))
(do ((row 0 (1+ row))) ((= row 9))
(exactly-one-number board col row)))
;; The standard Sudoku rules
(all-unique-values board (rows))
(all-unique-values board (cols))
(all-unique-values board (boxes))
;; Initially specified values
(read-sudoku
(open-input-file "input.sudoku")
board)
(let ((vals (solve-sat)))
(print-sudoku board vals)))
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