aoc2019/3.rkt

#lang racket

(define (parse-wire s)
  (map parse-seg (string-split (string-trim s) ",")))

(define wire-defs
       (string-split (string-trim (file->string "input.3.txt")) "\n"))

(define-struct seg (dir len))
(define-struct aseg (x1 y1 x2 y2))
(define-struct pt (x y))

(define (pa a) (list (aseg-x1 a) (aseg-y1 a) (aseg-x2 a) (aseg-y2 a)))
(define (pp p) (list (pt-x p) (pt-y p)))

(define (parse-seg str)
  (make-seg
   (string->symbol (substring str 0 1))
   (string->number (substring str 1))))

(define wires (map parse-wire wire-defs))

(define (make-norm-aseg x1 y1 x2 y2)
  (let ([nx1 (min x1 x2)]
        [nx2 (max x1 x2)]
        [ny1 (min y1 y2)]
        [ny2 (max y1 y2)])
    (make-aseg nx1 ny1 nx2 ny2)))

(define (seg->aseg seg x y)
  (let ([dx (* (seg-len seg)
               (match (seg-dir seg)
                 ['R 1]
                 ['L -1]
                 [_ 0]))]
        [dy (* (seg-len seg)
               (match (seg-dir seg)
                 ['U 1]
                 ['D -1]
                 [_ 0]))])
        (values (make-norm-aseg x y (+ x dx) (+ y dy)) (+ x dx) (+ y dy))))

(define (wire->asegwire wire)
  (define (wire->asegwire+ wire x y)
    (cond
      [(empty? wire) '()]
      [else (let-values ([(aseg newx newy) (seg->aseg (first wire) x y)])
              (cons aseg (wire->asegwire+ (rest wire) newx newy)))]))
  (wire->asegwire+ wire 0 0))

(define aseg-wires (map wire->asegwire wires))

(define (horiz? aseg)
  (= (aseg-y1 aseg) (aseg-y2 aseg)))
(define (vert? aseg)
  (= (aseg-x1 aseg) (aseg-x2 aseg)))

(define (cross aseg1 aseg2)
  (cond
    ;; both horizontal
    [(and (horiz? aseg1) (horiz? aseg2) (= (aseg-y1 aseg1) (aseg-y1 aseg2))
          (>= (aseg-x2 aseg2) (aseg-x1 aseg1))
          (<= (aseg-x1 aseg2) (aseg-x2 aseg1)))
     (list (make-pt (max (aseg-x1 aseg1) (aseg-x1 aseg2)) (aseg-y1 aseg1))
           (make-pt (min (aseg-x2 aseg1) (aseg-x2 aseg2)) (aseg-y1 aseg1)))]
    ;; both vertical
    [(and (vert? aseg1) (vert? aseg2) (= (aseg-x1 aseg1) (aseg-x1 aseg2))
          (>= (aseg-y2 aseg2) (aseg-y1 aseg1))
          (<= (aseg-y1 aseg2) (aseg-y2 aseg1)))
     (list (make-pt (aseg-x1 aseg1) (max (aseg-y1 aseg1) (aseg-y1 aseg2)))
           (make-pt (aseg-x1 aseg1) (min (aseg-y2 aseg1) (aseg-y2 aseg2))))]
    ;; h/v
    [(and (horiz? aseg1) (vert? aseg2)
          (>= (aseg-x1 aseg2) (aseg-x1 aseg1))
          (<= (aseg-x1 aseg2) (aseg-x2 aseg1))
          (>= (aseg-y1 aseg1) (aseg-y1 aseg2))
          (<= (aseg-y1 aseg1) (aseg-y2 aseg2)))
     (list (make-pt (aseg-x1 aseg2) (aseg-y1 aseg1)))]
    ;; v/h
    [(and (vert? aseg1) (horiz? aseg2)
          (>= (aseg-x1 aseg1) (aseg-x1 aseg2))
          (<= (aseg-x1 aseg1) (aseg-x2 aseg2))
          (>= (aseg-y1 aseg2) (aseg-y1 aseg1))
          (<= (aseg-y1 aseg2) (aseg-y2 aseg1)))
     (list (make-pt (aseg-x1 aseg1) (aseg-y1 aseg2)))]
    [else '()]))

(define (aseg-cross aseg wire)
  (cond
    [(empty? wire) '()]
    [else
     (append (cross aseg (first wire)) (aseg-cross aseg (rest wire)))]))

(define (get-crossings+ wire1 wire2)
  (cond
    [(empty? wire1) '()]
    [else (append (aseg-cross (first wire1) wire2) (get-crossings (rest wire1) wire2))]))

(define (get-crossings wire1 wire2)
  (filter (lambda (p) (not (and (zero? (pt-x p)) (zero? (pt-y p)))))
          (get-crossings+ wire1 wire2)))

(define crossings (get-crossings (first aseg-wires) (second aseg-wires)))

(define (manhattan pt)
  (+ (abs (pt-x pt)) (abs (pt-y pt))))

(define (min-crossing crs)
  (cond
    [(empty? crs) +inf.0]
    [else (min (manhattan (first crs)) (min-crossing (rest crs)))]))

;; Part 1
;; Holy SHIT i cannot believe this was actually the right answer WTF
;; i assumed i made some sort of typo in cross lol
;; UPDATE:
;; i had a bug where i forgot to have make-norm-aseg actually work
;; and THEN i also forgot to filter crossing '(0 0)
;; BUT this somehow didn't affect the answer for part 1
;; i just got screwed on part 2
;; anyway now both work
(displayln (min-crossing crossings))

(define (aseg-on-pt aseg pt)
  (or
   (and (= (pt-x pt) (aseg-x1 aseg) (aseg-x2 aseg))
        ;; yeah so i remembered that <= can take more than 2 args here
        ;; way before writing (cross)
        ;; huge oof
        (<= (aseg-y1 aseg) (pt-y pt) (aseg-y2 aseg)))
   (and (= (pt-y pt) (aseg-y1 aseg) (aseg-y2 aseg))
        (<= (aseg-x1 aseg) (pt-x pt) (aseg-x2 aseg)))))

(define (aseg-pt-dist aseg pt)
  (cond
    [(horiz? aseg) (- (pt-x pt) (aseg-x1 aseg))]
    [(vert? aseg) (- (pt-y pt) (aseg-y1 aseg))]))

(define (aseg-len aseg)
  (+
   (- (aseg-x2 aseg) (aseg-x1 aseg))
   (- (aseg-y2 aseg) (aseg-y1 aseg))))

(define (get-steps wire pt)
  (cond
    [(empty? wire) (error "thinking")]
    [else
     (cond
       [(aseg-on-pt (first wire) pt)
        (aseg-pt-dist (first wire) pt)]
       [else
        (+ (aseg-len (first wire)) (get-steps (rest wire) pt))])]))

(define (min-len-crossing crs wire1 wire2)
  (cond
    [(empty? crs) +inf.0]
    [else (min (+ (get-steps wire1 (first crs)) (get-steps wire2 (first crs)))
               (min-len-crossing (rest crs) wire1 wire2))]))

;; Part 2
(displayln (min-len-crossing crossings (first aseg-wires) (second aseg-wires)))