aoc2022/8.rkt

#lang curly-fn racket

(require "scripts/aoc.rkt")

;; solution for day 8

(define (g-ref grid y x)
  (vector-ref (vector-ref grid y) x))

(define (g-size grid)
  (values (vector-length grid) (vector-length (vector-ref grid 0))))

(define (part1 grid)
  (define-values [h w] (g-size grid))

  (define (visible? y x)
    (define v (g-ref grid y x))
    (cond
      [(= 0 y) #t]
      [(= 0 x) #t]
      [(= (sub1 h) y) #t]
      [(= (sub1 w) x) #t]
      [else
        (or
          (for/and ([x* (in-range 0 x)])
            (< (g-ref grid y x*) v))
          (for/and ([x* (in-range (add1 x) w)])
            (< (g-ref grid y x*) v))
          (for/and ([y* (in-range 0 y)])
            (< (g-ref grid y* x) v))
          (for/and ([y* (in-range (add1 y) h)])
            (< (g-ref grid y* x) v)))]))

  (for*/sum ([x (in-range w)] [y (in-range h)] #:when (visible? y x))
    1))

(define (part2 grid)
  (define-values [h w] (g-size grid))

  (define (scenic-score y x)
    (define v (g-ref grid y x))
    (*
      (for/sum ([x* (in-range (sub1 x) -1 -1)] #:final (>= (g-ref grid y x*) v))
        1)
      (for/sum ([x* (in-range (add1 x) w)] #:final (>= (g-ref grid y x*) v))
        1)
      (for/sum ([y* (in-range (sub1 y) -1 -1)] #:final (>= (g-ref grid y* x) v))
        1)
      (for/sum ([y* (in-range (add1 y) h)] #:final (>= (g-ref grid y* x) v))
        1)))

  (apply max
    (for*/list ([y (in-range h)] [x (in-range w)])
      (scenic-score y x))))

(define (parse fname)
  (for/vector ([line (in-list (file->lines fname))])
    (for/vector ([chr (in-list (string->list (string-trim line)))])
      (- (char->integer chr) (char->integer #\0)))))

(module+ main
  (define input (parse "inputs/8"))
  (answer 8 1 (time (part1 input)))
  (answer 8 2 (time (part2 input)))
  (displayln "meow"))