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56 lines
1.3 KiB
Racket
56 lines
1.3 KiB
Racket
#lang br
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(require racket/file rackunit)
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(define (stack cards)
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(reverse cards))
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(define (cut n cards)
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(define-values (head tail)
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(split-at cards (match n
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[(? positive?) n]
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[_ (- (length cards) (abs n))])))
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(append tail head))
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(define (increment n cards)
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(define len (length cards))
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(define vec (make-vector len))
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(for ([(card idx) (in-indexed cards)])
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(vector-set! vec (modulo (* idx n) len) card))
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(vector->list vec))
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(define (run program [deck-size 10])
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(for/fold ([cards (range deck-size)])
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([ln (in-list (string-split program "\n"))])
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(match (string-split ln)
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[(list "cut" (app string->number num)) (cut num cards)]
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[(list _ _ "increment" (app string->number num)) (increment num cards)]
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[_ (stack cards)])))
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(check-equal?
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(run "deal with increment 7
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deal into new stack
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deal into new stack")
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'(0 3 6 9 2 5 8 1 4 7))
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(check-equal?
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(run "cut 6
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deal with increment 7
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deal into new stack")
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'(3 0 7 4 1 8 5 2 9 6))
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(check-equal?
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(run "deal into new stack
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cut -2
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deal with increment 7
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cut 8
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cut -4
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deal with increment 7
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cut 3
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deal with increment 9
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deal with increment 3
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cut -1")
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'(9 2 5 8 1 4 7 0 3 6))
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;; 1
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(check-eq? (index-of (run (file->string "22.rktd") 10007) 2019) 4086)
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