25 lines
514 B
Scheme
25 lines
514 B
Scheme
;; $ csc day17.scm -o day17 -O5
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;; $ ./day17 -:hm8g
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(use srfi-1)
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(declare (fixnum))
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(define (prepend! x list)
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(set-cdr! list (cons (car list) (cdr list)))
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(set-car! list x))
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(define (spin steps n after)
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(let ((buffer (circular-list 0)))
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(do ((i 1 (+ i 1)))
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((> i n) (cadr (member after buffer)))
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(let ((new (drop buffer (+ steps 1))))
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(prepend! i new)
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(set! buffer new)))))
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(write (spin 3 2017 2017))
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(newline)
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(write (spin 312 2017 2017))
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(newline)
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(write (spin 312 50000000 0))
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(newline)
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