blob: 7a3a5cab4f358669ea41178b093af32ef2300cb9 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
|
#lang racket
(require "../../jj-aoc.rkt"
threading)
(define sea-floor
(for*/hash ([(row i) (in-indexed (in-lines (open-day 25 2021)))] [(c j) (in-indexed row)])
(values (list i j) c)))
(define-values (max-i max-j)
(~> sea-floor hash-keys (argmax (λ (coord) (apply + coord)) _) (apply values _)))
(define (cucumber-movement h c delta-i delta-j)
(define new-hash (hash-copy h))
(for* ([(coord x) (in-hash h)] #:when (eq? x c))
(match-define (list i j) coord)
(define neighbor (list (+ delta-i i) (+ delta-j j)))
(define neighbor-or-wrap
(if (hash-has-key? h neighbor) neighbor (list (if (= delta-i 0) i 0) (if (= delta-j 0) j 0))))
(when (eq? #\. (hash-ref h neighbor-or-wrap))
(hash-set*! new-hash coord #\. neighbor-or-wrap c)))
new-hash)
(define (eastwards-movement h)
(cucumber-movement h #\> 0 1))
(define (southwards-movement h)
(cucumber-movement h #\v 1 0))
;; part 1
(for/fold ([f sea-floor] [step 0] #:result (add1 step)) ([i (in-naturals 1)])
(define f* (~> f eastwards-movement southwards-movement))
#:break (equal? f* f)
(values f* i))
;; no part 2 -- merry Christmas
|
