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#lang racket
(require "../../jj-aoc.rkt"
threading
(only-in algorithms chunks-of)
racket/hash)
(define directions
(for/list ([l (in-input-port-chars (open-day 3 2015))])
(string->symbol (string l))))
(define (trace-santa dirs)
(define visits (make-hash))
(for/fold ([x 0] [y 0] #:result visits) ([dir (in-list dirs)])
(hash-set! visits `(,x ,y) #true)
(match dir
['^ (values x (add1 y))]
['v (values x (sub1 y))]
['< (values (add1 x) y)]
['> (values (sub1 x) y)])))
;; part 1
(~> directions trace-santa hash-values length)
;; part 2
(~> directions (chunks-of 2) (apply map list _) (map trace-santa _) (match-define (list real robo) _))
(hash-union! real robo #:combine (λ _ #true))
(~> real hash-values length)
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