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author | Hunky Jimpjorps <thechairman@thechairman.info> | 2024-02-02 17:05:12 -0500 |
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committer | Hunky Jimpjorps <thechairman@thechairman.info> | 2024-02-02 17:05:12 -0500 |
commit | 48e35ad3b0b0c62f936784e4aca70b17c3b0e3f9 (patch) | |
tree | f59a13e0b5e80ab925220b4488c6e36b1bec660a /aoc2023-racket/day-09/day-09.rkt | |
parent | 87e9ab25ff70e215b537939a4bc23ab101f41dbe (diff) | |
download | gleam_aoc-48e35ad3b0b0c62f936784e4aca70b17c3b0e3f9.tar.gz gleam_aoc-48e35ad3b0b0c62f936784e4aca70b17c3b0e3f9.zip |
renaming
Diffstat (limited to 'aoc2023-racket/day-09/day-09.rkt')
-rw-r--r-- | aoc2023-racket/day-09/day-09.rkt | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/aoc2023-racket/day-09/day-09.rkt b/aoc2023-racket/day-09/day-09.rkt new file mode 100644 index 0000000..5eda1eb --- /dev/null +++ b/aoc2023-racket/day-09/day-09.rkt @@ -0,0 +1,32 @@ +#lang racket + +(require advent-of-code + threading) + +(define histories + (for/list ([raw-history (in-lines (open-aoc-input (find-session) 2023 9 #:cache #true))]) + (~>> raw-history + string-split + (map string->number)))) + +(define (constant? xs) + (= 1 (length (remove-duplicates xs)))) + +(define/match (derivative xs) + [((list a b)) (list (- b a))] + [((list* a b _)) (cons (- b a) (derivative (rest xs)))]) + +(define (extrapolate xs) + (if (constant? xs) + (car xs) + (+ (last xs) (extrapolate (derivative xs))))) + +;; part 1 +(~>> histories + (map extrapolate) + (apply +)) + +;; part 2 +(~>> histories + (map (λ~> reverse extrapolate)) + (apply +)) |