diff options
Diffstat (limited to '2021')
| -rw-r--r-- | 2021/day-12/day-12.rkt | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/2021/day-12/day-12.rkt b/2021/day-12/day-12.rkt new file mode 100644 index 0000000..0b1f414 --- /dev/null +++ b/2021/day-12/day-12.rkt @@ -0,0 +1,52 @@ +#lang racket +(require "../../jj-aoc.rkt" + threading) + +(define path-pairs + (for/list ([l (in-lines (open-day 12 2021))]) + (match (string-split l "-") + [(list start end) (cons start end)]))) + +(define edges-hash (make-hash)) + +(for ([pair (in-list path-pairs)]) + (match-define (cons start end) pair) + (hash-update! edges-hash + start + (curry cons end) + '()) + (hash-update! edges-hash + end + (curry cons start) + '())) + +;; part 1 +(define (backtracking-allowed? next prevs) + (and (equal? (string-downcase next) next) + (member next prevs))) + +(define (look-for-next-cave + [path-list '("start")] + #:two-visits? [visit-used-up? #t]) + (define current-cave (car path-list)) + (cond + [(equal? current-cave "end") (list path-list)] + [else + (~>> (for/list ([next-path (in-list (hash-ref edges-hash current-cave null))] + #:unless (equal? next-path "start") + #:when (not (and (backtracking-allowed? next-path path-list) + visit-used-up?))) + (look-for-next-cave + (cons next-path path-list) + #:two-visits? (or (backtracking-allowed? next-path path-list) + visit-used-up?))) + (apply append))])) + +(~> (look-for-next-cave) + length + time) + +;; part 2 +(~> (look-for-next-cave #:two-visits? #f) + length + time)
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