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aoc-racket/2019/20.rkt

34 lines
1.2 KiB
Racket

5 years ago
#lang br
(require racket/file rackunit racket/set graph)
(define str (file->string "20.rktd"))
(define (find-cells pred)
(for*/hasheqv ([(row ridx) (in-indexed (string-split str "\n"))]
[(c cidx) (in-indexed row)]
#:when (pred c))
(values (make-rectangular cidx ridx) c)))
(define passage-locs (find-cells (λ (c) (char=? c #\.))))
(define letter-locs (find-cells char-alphabetic?))
(define g (unweighted-graph/undirected null))
(for* ([loc (in-hash-keys passage-locs)]
[delta (list 1 -1 +i -i)])
(when (hash-has-key? passage-locs (+ loc delta))
(add-edge! g loc (+ loc delta)))
(when (hash-has-key? letter-locs (+ loc delta))
(add-edge! g loc (string->symbol
(apply string ((if (member delta (list -1 -i))
reverse
values) (for/list ([d (list delta (* 2 delta))])
(hash-ref letter-locs (+ loc d)))))))))
(for ([v (in-vertices g)]
#:when (and (symbol? v) (not (memq v '(AA ZZ)))))
(apply add-edge! g (get-neighbors g v)))
;; 1
(check-eq? (- (length (fewest-vertices-path g 'AA 'ZZ)) 3) 638)