From 7946946bd77399e3f634739d5790a25c0ef8fadf Mon Sep 17 00:00:00 2001
From: Jonathan Chan <jcxz@cs.ubc.ca>
Date: Fri, 11 Dec 2020 11:02:08 -0800
Subject: [PATCH] Refactored Day 11 for performance.

---
 src/11.rkt | 37 ++++++++++++++++++++++---------------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/src/11.rkt b/src/11.rkt
index 5639898..f58da51 100644
--- a/src/11.rkt
+++ b/src/11.rkt
@@ -1,20 +1,13 @@
 #lang curly-fn racket
 
-(require "../lib.rkt")
+(require threading
+         "../lib.rkt")
 
 (define input (lists->vectors (map string->list (problem-input 11))))
 (define width (vector-length (vector-ref input 0)))
 (define length (vector-length input))
 
-(define (neighbours seats r c)
-  (count
-   #{char=? % #\#}
-   (for*/list ([r* (in-range (max 0 (sub1 r)) (min (+ r 2) length))]
-               [c* (in-range (max 0 (sub1 c)) (min (+ c 2) width))]
-               #:unless (and (= r r*) (= c c*)))
-     (vector-ref (vector-ref seats r*) c*))))
-
-(define (visible-in seats r c dr dc)
+(define (first-seat r c dr dc)
   (define rs
     (cond
       [(positive? dr) (in-range r length dr)]
@@ -28,13 +21,27 @@
   (for/or ([r* rs]
            [c* cs]
            #:unless (and (= r r*) (= c c*)))
-    (define seat (vector-ref (vector-ref seats r*) c*))
-    #:final (member seat '(#\L #\#))
-    (char=? seat #\#)))
+    (define seat (vector-ref (vector-ref input r*) c*))
+    (and (member seat '(#\L #\#))
+         (list r* c*))))
+
+(define first-seats
+  (for*/hash ([r (in-range 0 length)]
+              [c (in-range 0 width)])
+    (values (list r c)
+            (filter-map (match-lambda [`(,dr ,dc) (first-seat r c dr dc)])
+                        '((-1 -1) (-1 0) (-1 1) (0 -1) (0 1) (1 -1) (1 0) (1 1))))))
+
+(define (neighbours seats r c)
+  (for*/sum ([r* (in-range (max 0 (sub1 r)) (min (+ r 2) length))]
+             [c* (in-range (max 0 (sub1 c)) (min (+ c 2) width))]
+             #:unless (and (= r r*) (= c c*)))
+    (if (char=? (vector-ref (vector-ref seats r*) c*) #\#) 1 0)))
 
 (define (visible seats r c)
-  (count (match-lambda [`(,dr ,dc) (visible-in seats r c dr dc)])
-         '((-1 -1) (-1 0) (-1 1) (0 -1) (0 1) (1 -1) (1 0) (1 1))))
+  (count
+   (match-lambda [`(,r* ,c*) (char=? (vector-ref (vector-ref seats r*) c*) #\#)])
+   (hash-ref first-seats (list r c))))
 
 (define (step-seats counter die seats)
   (let ([new-seats (vector-map vector-copy (vector-copy seats))])