56 lines
1.8 KiB
Racket
56 lines
1.8 KiB
Racket
#lang curly-fn racket
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(require "scripts/aoc.rkt")
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;; solution for day 3
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(define *delta* '((0 . 1) (1 . 1) (1 . 0)
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(1 . -1) (0 . -1) (-1 . -1)
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(-1 . 0) (-1 . 1)))
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(define (posn+ a b)
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(cons (+ (car a) (car b))
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(+ (cdr a) (cdr b))))
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(define (part1 input)
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(define numbers
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(for/set ([(pos elem) (in-hash input)]
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#:when (char? elem)
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[d (in-list *delta*)]
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#:do [(define neigh (hash-ref input (posn+ pos d) #f))]
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#:when (list? neigh))
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neigh))
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(for/sum ([n (in-set numbers)])
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(third n)))
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(define (part2 input)
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(for/sum ([(pos elem) (in-hash input)]
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#:when (equal? elem #\*)
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#:do [(define neighs
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(for/set ([d (in-list *delta*)]
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#:do [(define neigh (hash-ref input (posn+ pos d) #f))]
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#:when (list? neigh))
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neigh))]
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#:when (= 2 (set-count neighs)))
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(apply * (map third (set->list neighs)))))
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(define (parse fname)
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(define elements (make-hash))
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(for ([line (in-lines (open-input-file fname))] [y (in-naturals)]
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#:do [(for ([posn (in-list (regexp-match-positions* #px"[0-9]+" line))]
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#:do [(match-define (cons xmin xmax) posn)]
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[x (in-range xmin xmax)])
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(hash-set! elements (cons y x)
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(list y xmin (string->number (substring line xmin xmax)))))]
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[chr (in-string line)] [x (in-naturals)]
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#:unless (equal? chr #\.)
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#:unless (char-numeric? chr))
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(hash-set! elements (cons y x) chr))
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elements)
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(module+ main
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(define input (parse "inputs/3"))
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(answer 3 1 (time (part1 input)))
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(answer 3 2 (time (part2 input)))
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(displayln "meow"))
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