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#lang racket
(require advent-of-code
threading
data/applicative
data/monad
megaparsack
megaparsack/text)
(struct claim (number start-x start-y size-x size-y) #:transparent)
(define claim/p
(do (char/p #\#)
[number <- integer/p]
(string/p " @ ")
[start-x <- integer/p]
(char/p #\,)
[start-y <- integer/p]
(string/p ": ")
[size-x <- integer/p]
(char/p #\x)
[size-y <- integer/p]
(pure (claim number start-x start-y size-x size-y))))
(define (parse-claim str)
(parse-result! (parse-string claim/p str)))
(define (make-claim ht cl)
(for*/fold ([fabric ht])
([x (in-range (claim-start-x cl) (+ (claim-start-x cl) (claim-size-x cl)))]
[y (in-range (claim-start-y cl) (+ (claim-start-y cl) (claim-size-y cl)))])
(hash-update fabric (cons x y) add1 0)))
(define claims
(~> (port->lines (open-aoc-input (find-session) 2018 3 #:cache #true)) (map parse-claim _)))
(define claimed-fabric
(for/fold ([fabric (hash)]) ([cl (in-list claims)])
(make-claim fabric cl)))
;; part 1
(for/sum ([claim-count (in-list (hash-values claimed-fabric))] #:when (< 1 claim-count)) 1)
;; part 2
(define (uncontested-claim? fabric cl)
(for*/and ([x (in-range (claim-start-x cl) (+ (claim-start-x cl) (claim-size-x cl)))]
[y (in-range (claim-start-y cl) (+ (claim-start-y cl) (claim-size-y cl)))])
(= 1 (hash-ref fabric (cons x y)))))
(for/first ([cl (in-list claims)] #:when (uncontested-claim? claimed-fabric cl))
(claim-number cl))
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