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aoc-racket/2018/05.rkt

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#lang debug br
(require racket/file racket/set)
(define fp (open-input-file "05.txt"))
(define fpbs (port->bytes fp))
(define-macro (for/mutable-list (SEQ ...) . BODY)
#'(let loop ([mprs null][xs (reverse (for/list (SEQ ...) . BODY))])
(if (empty? xs)
mprs
(loop (mcons (car xs) mprs) (cdr xs)))))
(define (reactive-pair? mprs)
(= 32 (abs (- (mcar (mcdr mprs)) (mcar (mcdr (mcdr mprs)))))))
(define (react [fpbs fpbs])
(define mprs0 (mcons #f (for/mutable-list ([b (in-bytes fpbs)])
b)))
(let loop ([mprs mprs0][found? #false])
(cond
[(or (empty? mprs)
(empty? (mcdr mprs))
(empty? (mcdr (mcdr mprs))))
(if found? (loop mprs0 #false) mprs0)]
[(reactive-pair? mprs)
(set-mcdr! mprs (mcdr (mcdr (mcdr mprs))))
(loop (mcdr mprs) #true)]
[else (loop (mcdr mprs) found?)]))
(for/sum ([val (in-mlist (mcdr mprs0))])
1))
(define ()
(react fpbs))
(define possible-units
(map char->integer (remove-duplicates (map char-upcase (map integer->char (bytes->list fpbs))) char=?)))
(define (remove-unit fbps unit)
(regexp-replace* (regexp (format "[~a~a]" (integer->char unit) (integer->char (+ unit 32)))) fbps ""))
(define (★★)
(apply min (for/list ([unit (in-list possible-units)])
(react (remove-unit fpbs unit)))))
(module+ test
(require rackunit)
(check-equal? (time ()) 10564)
(check-equal? (time (★★)) 6336))