57 lines
1.6 KiB
Racket
57 lines
1.6 KiB
Racket
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#lang curly-fn racket
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(require "scripts/aoc.rkt")
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;; solution for day 8
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(define (follow mapl cur inst)
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(define node
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(for/first ([entry (in-list mapl)]
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#:when (equal? (first entry) cur))
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entry))
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(match inst
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[#\L (second node)]
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[#\R (third node)]))
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(define (part1 input)
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(for/fold ([cur "AAA"] [cnt 0] #:result cnt)
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([inst (in-cycle (in-list (first input)))])
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#:break (equal? cur "ZZZ")
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(define next (follow (second input) cur inst))
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(values next (add1 cnt))))
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(define (part2 input)
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(define all-as
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(for/list ([x (in-list (second input))] #:when (regexp-match? #px"^..A$" (first x)))
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(first x)))
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(define (end-z? c)
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(regexp-match? #px"^..Z$" c))
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(define (run-item item)
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(for/fold ([cur item] [cnt 0] #:result cnt)
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([inst (in-cycle (in-list (first input)))])
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#:break (end-z? cur)
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(define next (follow (second input) cur inst))
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(values next (add1 cnt))))
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(apply lcm (map run-item all-as)))
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(define (parse fname)
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(match-define (list instl mapl) (string-split (file->string fname) "\n\n"))
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(list (string->list instl)
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(for/list ([line (in-list (string-split mapl "\n"))])
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(match-define (pregexp #px"([A-Z0-9]{3}) = .([A-Z0-9]{3}), ([A-Z0-9]{3})."
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(list _ node left right))
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line)
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(list node left right))))
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; (part2 (parse "inputs/8-test1"))
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; (error)
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(module+ main
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(define input (parse "inputs/8"))
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(answer 8 1 (time (part1 input)))
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(answer 8 2 (time (part2 input)))
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(displayln "meow"))
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