Nクイーン高速化

fast.scm

#!/usr/local/bin/gosh

(define (solve? num ls)
  (let loop ((ls ls)(n 1))
	(cond
	  ((null? ls)#t)
	  ((= (abs (- num (car ls))) n)
	   #f)
	  (else (loop (cdr ls)(+ n 1))))))

(define (check? lst)
  (let loop ((lst lst))
	(cond
	  ((null? (cdr lst))#t)
	  ((solve? (car lst) (cdr lst))
	   (loop (cdr lst)))
	  (else #f))))

(define (queen lst)
  (let loop ((lst lst)(result '()))
	(if (null? lst)
	  (print (reverse result))
	  (for-each (lambda(x)
		(if (check? (reverse (cons x result)))
		          (loop (delete x lst) (cons x result)))) lst))))

;(time (queen '(0 1 2 3 4 5 6 7)))
; real 0.008
; user 0.010
; sys 0.000