37 lines
879 B
Scheme
37 lines
879 B
Scheme
;;; NQUEENS -- Compute number of solutions to 8-queens problem.
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(define trace? #f)
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(define (nqueens n)
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(define (_1-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 (my-try x y z)
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(if (null? x)
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(if (null? y)
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(begin (if trace? (begin (write z) (newline))) 1)
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0)
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(+ (if (ok? (car x) 1 z)
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(my-try (append (cdr x) y) '() (cons (car x) z))
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0)
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(my-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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(my-try (_1-to n) '() '()))
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(define (main)
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(run-benchmark
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"nqueens"
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nqueens-iters
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(lambda (result) (equal? result 92))
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(lambda (n) (lambda () (nqueens n)))
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8))
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