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35 lines
713 B
Scheme
35 lines
713 B
Scheme
;(cond-expand
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; (cyclone
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; (import
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; (scheme base)
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; (scheme write))
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; )
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; (else #f))
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(define (nqueens n)
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(define (dec-to n)
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(let loop ((i n) (l '()))
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(if (= i 0) l (loop (- i 1) (cons i l)))))
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(define (try x y z)
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(if (null? x)
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(if (null? y)
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1
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0)
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(+ (if (ok? (car x) 1 z)
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(try (append (cdr x) y) '() (cons (car x) z))
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0)
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(try (cdr x) (cons (car x) y) z))))
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(define (ok? row dist placed)
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(if (null? placed)
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#t
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(and (not (= (car placed) (+ row dist)))
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(not (= (car placed) (- row dist)))
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(ok? row (+ dist 1) (cdr placed)))))
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(try (dec-to n) '() '()))
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(write
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(nqueens 8))
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