2019/src/11.rkt

#lang plai

(require "../lib.rkt"
         "IntCode.rkt")

(define input
  (string->program (car (problem-input 11))))

;; 0 is a "black" panel and 1 is a "white" panel
;; but the spaceship is entirely black
;; so the identifier colour is in "white"
;; which we show as black blocks against white
(define panel-hash
  (make-hash '((0 . #\ ) (1 . #\█))))

;; The hull as a hash (x . y) -> c
;; x increases rightward
;; y increases downward
(define hull (make-hash))

;; The hull as a vector of row vectors of c
;; i.e. x = index of inner vectors,
;;      y = index of outer vector
(define (make-grid xrange yrange)
  (build-vector
   (add1 yrange)
   (λ (_) (make-vector (add1 xrange)))))

;; Turn CCW if δ = 0, CW if δ = 1
(define (update-dir dir δ)
  (match dir
    ['U (if (zero? δ) 'L 'R)]
    ['D (if (zero? δ) 'R 'L)]
    ['L (if (zero? δ) 'D 'U)]
    ['R (if (zero? δ) 'U 'D)]))

;; Move in given direction (up/down/left/right)
(define (update-pos dir xy)
  (let ([x (car xy)]
        [y (cdr xy)])
    (match dir
      ['U (cons x (sub1 y))]
      ['D (cons x (add1 y))]
      ['L (cons (sub1 x) y)]
      ['R (cons (add1 x) y)])))

;; Deploy the emergency hull painting robot!
(define (deploy st dir xy)
  (define clr (hash-ref hull xy 0))
  (type-case state st
    [halt (_) (void)]
    [in (resume)
        (let*-values
            ([(clr* st) (resume-with-output (resume clr))]
             [(δ st)    (resume-with-output st)])
          (cond [(!= clr clr*)
                 (hash-set! hull xy clr*)])
          (let* ([dir (update-dir dir δ)]
                 [xy  (update-pos dir xy)])
            (deploy st dir xy)))]
    [else (error "Unexpected program state.")]))

(define (part1)
  (deploy (exec input) 'U '(0 . 0))
  (hash-count hull))

(define (part2)
  (set! hull (make-hash '(((0 . 0) . 1))))
  (deploy (exec input) 'U '(0 . 0))
  (show-hash-grid panel-hash hull) #f)

(show-solution (part1) (part2))