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1 files changed, 51 insertions, 0 deletions

diff --git a/racket/aoc2018/day-03/day-03.rkt b/racket/aoc2018/day-03/day-03.rkt
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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))