blob: b5478eb67014ad5ff1be5b50be96d2215fd74589 (
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
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
|
#lang racket
(require advent-of-code
threading
simple-polynomial
racket/hash)
(define input (fetch-aoc-input (find-session) 2023 21 #:cache #true))
(define initial-garden
(~> (for*/list ([(row r) (in-indexed (string-split input "\n"))]
[(col c) (in-indexed row)]
#:unless (equal? col #\#))
(cons (cons r c) (if (equal? col #\S) 'on 'off)))
make-hash))
(define (neighbors p)
(match-define (cons r c) p)
(list (cons (add1 r) c) (cons (sub1 r) c) (cons r (add1 c)) (cons r (sub1 c))))
(define (make-n-steps garden n)
(define g (hash-copy garden))
(define (make-one-step)
(define update (make-hash))
(for ([(cons state) (in-hash g)] #:when (equal? state 'on))
(hash-set! update cons 'off)
(for ([neighbor (in-list (neighbors cons))] #:when (hash-has-key? g neighbor))
(hash-set! update neighbor 'on)))
(hash-union! g update #:combine/key (λ (_k _v v) v)))
(for/fold ([_ void]
#:result (~>> g hash-values (count (curry equal? 'on))))
([i (in-range n)])
(displayln i)
(make-one-step)))
;; part 1
(make-n-steps initial-garden 64)
;; part 2
;; the growth of the steps pattern is regular and quadratic
;; the rock pattern has aisles in it that allow the steps pattern to expand freely
;; such that it will cross from one side to another in X steps
;; where X is the height/width of the repeated section
(define grid-size (~> input (string-split "\n") length))
(define half-size (/ (sub1 grid-size) 2))
(define expanded-garden
(~> (for*/list (#:do [(define rows (string-split input "\n"))]
#:do [(define height (length rows))]
[(row r) (in-indexed rows)]
#:do [(define width (string-length row))]
[(col c) (in-indexed row)]
#:unless (equal? col #\#)
[n (in-inclusive-range -3 3)]
[m (in-inclusive-range -3 3)])
(cons (cons (+ r (* n height)) (+ c (* m width)))
(if (and (= n m 0) (equal? col #\S)) 'on 'off)))
make-hash))
(define fitting-points
(for/list ([n (in-range 3)] #:do [(define size (+ half-size (* n grid-size)))])
(cons n (make-n-steps expanded-garden size))))
(define end-cycle 26501365)
(define x (/ (- end-cycle half-size) grid-size))
((points->polynomial fitting-points) x)
|
