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#lang racket
(require "../../jj-aoc.rkt"
threading
graph)
(define data
(for/fold ([cells (hash)])
([row (in-lines (open-day 15 2021))]
[x (in-naturals)])
(for/fold ([cells cells])
([n (in-string row)]
[y (in-naturals)])
(hash-set cells
`(,x ,y)
(~> n string string->number)))))
(define x-max (~>> data hash-keys (map first) (apply max)))
(define y-max (~>> data hash-keys (map second) (apply max)))
(define (neighbors pt d)
(match-define (list x y) pt)
(~>> (list (list (add1 x) y)
(list (sub1 x) y)
(list x (add1 y))
(list x (sub1 y)))
(filter (curry hash-has-key? d))))
(define (grid-graph d)
(weighted-graph/directed
(for*/list ([coord (in-list (hash-keys d))]
[neighbor (in-list (neighbors coord d))]
[weight (in-value (hash-ref d neighbor))])
(list weight coord neighbor))))
;; part 1
(define (find-path-weight d)
(define grid (grid-graph d))
(let-values ([(node-distances _) (dijkstra grid '(0 0))])
(define xm (~>> d hash-keys (map first) (apply max)))
(define ym (~>> d hash-keys (map second) (apply max)))
(hash-ref node-distances (list xm ym))))
(~> data
find-path-weight
time)
;; part 2
(define nine-cycle
(in-cycle (inclusive-range 1 9)))
(define (expand-data data)
(for/fold ([cells (hash)])
([coord (in-list (hash-keys data))])
(match-define (list x y) coord)
(for*/fold ([cells cells])
([n (in-range 5)]
[m (in-range 5)]
[val (in-value (hash-ref data coord))])
(hash-set cells
(list (+ x (* n (add1 x-max)))
(+ y (* m (add1 y-max))))
(sequence-ref nine-cycle (+ val n m -1))))))
(~> data
expand-data
find-path-weight
time)
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