aoc2020/12.rkt

#lang curly-fn racket

(require "scripts/aoc.rkt")

;; solution for day 12

;; helper functions here

(define (d->r deg)
  (* (/ deg 180) pi))

(define (part1 input)
  (define-values [dir x y]
  (for/fold ([dir 0] [x 0] [y 0]) ([ins (in-list input)])
    (match-define (cons ltr num) ins)
    (match ltr
      ["N" (values dir x (+ y num))]
      ["S" (values dir x (- y num))]
      ["E" (values dir (+ x num) y)]
      ["W" (values dir (- x num) y)]
      ["L" (values (+ dir (d->r num)) x y)]
      ["R" (values (- dir (d->r num))  x y)]
      ["F" (values dir (+ x (* num (cos dir))) (+ y (* num (sin dir))))])))
  (inexact->exact (floor (+ (abs x) (abs y)))))

(define (part2 input)
  (define (rot x y d)
    (values
      (- (* x (cos d)) (* y (sin d)))
      (+ (* x (sin d)) (* y (cos d)))))
  (define-values [sx sy wx wy]
    (for/fold ([sx 0] [sy 0] [wx 10] [wy 1]) ([ins (in-list input)])
      (match-define (cons ltr num) ins)
      (match ltr
        ["N" (values sx sy wx (+ wy num))]
        ["S" (values sx sy wx (- wy num))]
        ["E" (values sx sy (+ wx num) wy)]
        ["W" (values sx sy (- wx num) wy)]
        ["L"
         (define-values [nwx nwy] (rot wx wy (d->r num)))
         (values sx sy nwx nwy)]
        ["R"
         (define-values [nwx nwy] (rot wx wy (d->r (- num))))
         (values sx sy nwx nwy)]
        ["F"
         (values (+ sx (* num wx)) (+ sy (* num wy)) wx wy)])))
  (inexact->exact (floor (+ (abs sx) (abs sy)))))

(module+ test
  (require rackunit)
  ;; tests here
  (displayln "no tests :("))

(module+ main
  (define input
    (for/list ([line (in-list (file->lines "inputs/12"))])
      (match line
        [(pregexp #px"^(.)([0-9]+)$" (list _ dir (app string->number num)))
         (cons dir num)])))
  ;; part 1
  (answer 12 1 (part1 input))

  ;; part 2
  (answer 12 2 (part2 input))

  (displayln "meow"))