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#lang racket
(require advent-of-code
threading)
(struct posn (x y) #:transparent)
(struct dir (x y) #:transparent)
(define/match (left _d)
[((dir 0 1)) (dir -1 0)]
[((dir -1 0)) (dir 0 -1)]
[((dir 0 -1)) (dir 1 0)]
[((dir 1 0)) (dir 0 1)])
(define/match (right _d)
[((dir 0 1)) (dir 1 0)]
[((dir 1 0)) (dir 0 -1)]
[((dir 0 -1)) (dir -1 0)]
[((dir -1 0)) (dir 0 1)])
(define/match (go _from _d _dist)
[((posn x y) (dir dx dy) dist) (posn (+ x (* dx dist)) (+ y (* dy dist)))])
(define input (~> (fetch-aoc-input (find-session) 2016 1 #:cache #true) string-trim (string-split ", ")))
;; part 1
(for/fold ([p (posn 0 0)]
[d (dir 0 1)]
#:result (+ (abs (posn-x p)) (abs (posn-y p))))
([instruction (in-list input)])
(displayln (~a p " " d))
(match instruction
[(regexp #rx"L(.*)" (list _ n)) (values (go p (left d) (string->number n))
(left d))]
[(regexp #rx"R(.*)" (list _ n)) (values (go p (right d) (string->number n))
(right d))]))
;; part 2
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