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#lang racket
(require advent-of-code
threading
fancy-app
racket/hash)
(define/match (instruction-parse _str)
[((regexp #px"(.)(.+)" (list _ (app string->symbol dir) (app string->number amt)))) (cons dir amt)])
(define (wire-parse str)
(~> str (string-split ",") (map instruction-parse _)))
(define wires
(~>> (fetch-aoc-input (find-session) 2019 3 #:cache #true) string-split (map wire-parse)))
(define (manhattan-distance-from-origin p)
(+ (abs (car p)) (abs (cdr p))))
(define (trace-wire-path wire)
(for/fold ([path (hash)] [x 0] [y 0] [len 0] #:result path) ([inst (in-list wire)])
(define-values (x* y*)
(match inst
[(cons 'U dy) (values x (+ y dy))]
[(cons 'D dy) (values x (- y dy))]
[(cons 'R dx) (values (+ x dx) y)]
[(cons 'L dx) (values (- x dx) y)]))
(define next-segment
(for*/list ([new-x (inclusive-range x x* (if (< x x*) 1 -1))]
[new-y (inclusive-range y y* (if (< y y*) 1 -1))])
(cons new-x new-y)))
(define numbered-segments
(for/hash ([segment (in-list next-segment)] [new-len (in-naturals len)])
(values segment new-len)))
(values (hash-union path numbered-segments #:combine (λ (v0 _) v0)) x* y* (+ len (cdr inst)))))
;; part 1
(define wire-paths (map trace-wire-path wires))
(define intersections
(~>> wire-paths
(map (λ~> hash-keys list->set))
(apply set-intersect)
(set-remove _ '(0 . 0))
set->list))
(~>> intersections (map manhattan-distance-from-origin) (apply min))
;; part 2
(~>> (for/list ([intersection (in-list intersections)])
(~>> wire-paths (map (hash-ref _ intersection)) (apply +)))
(apply min))
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