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47 lines
1.7 KiB
Racket
47 lines
1.7 KiB
Racket
#lang racket
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(require rackunit)
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(provide read-syntax)
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(define (str->visits str)
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(define start '(0 0))
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(define moves (map (λ(move) (case move
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[("^") '(0 1)]
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[("v") '(0 -1)]
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[("<") '(-1 0)]
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[(">") '(1 0)]))
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(regexp-match* #rx"." str)))
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(reverse (for/fold ([visit-acc (list start)])
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([move (in-list moves)])
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(cons (map + move (car visit-acc)) visit-acc))))
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(define (str->unique-visits str)
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(define visits (str->visits str))
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(length (remove-duplicates visits)))
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(define (str->robosanta str)
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(define-values (reversed-santa-path reversed-robo-path)
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(for/fold ([santa-acc empty][robo-acc empty])
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([c (in-string str)][pos (in-naturals)])
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(if (even? pos)
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(values (cons c santa-acc) robo-acc)
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(values santa-acc (cons c robo-acc)))))
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(define santa-str (string-append* (map ~a (reverse reversed-santa-path))))
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(define robo-str (string-append* (map ~a (reverse reversed-robo-path))))
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(length (remove-duplicates (append (str->visits santa-str) (str->visits robo-str)))))
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(check-equal? (str->unique-visits ">") 2)
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(check-equal? (str->unique-visits "^>v<") 4)
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(check-equal? (str->robosanta "^v") 3)
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(check-equal? (str->robosanta "^>v<") 3)
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(check-equal? (str->robosanta "^v^v^v^v^v") 11)
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(define (read-syntax source-path-string in-port)
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(with-syntax ([source-str (string-trim (port->string in-port))]
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[str->unique-visits str->unique-visits]
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[str->robosanta str->robosanta])
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#'(module _ racket
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(str->unique-visits source-str)
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(str->robosanta source-str)))) |