Add Advent 2021 - day 11.

2021/day11/p.rkt

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+#lang racket/base
+(require racket/match)
+
+(define (char->number c)
+  (string->number (string c)))
+
+(define (make-line t)
+  (list->vector (map char->number (string->list t))))
+
+(define sv (for/vector ([t (in-lines)]) (make-line t)))
+
+(define v (vector-length sv))
+(define h (vector-length (vector-ref sv 0)))
+
+(define (access pv ph)
+  (vector-ref (vector-ref sv pv) ph))
+(define (change pv ph v)
+  (vector-set! (vector-ref sv pv) ph v))
+
+(define (apply-step i)
+  ; keep track of octopuses that have flashed
+  (define index 0)
+  (define nines (make-vector 300 null)) ; arbitrary length
+  (define (try-add-nine pv ph)
+    (when (= (access pv ph) 9)
+      (vector-set! nines index (cons pv ph))
+      (set! index (add1 index)))
+    (change pv ph (add1 (access pv ph))))
+
+  (for* ([vi (in-range v)] [hi (in-range h)])
+    (when (> (access vi hi) 9) (change vi hi 0)) ; optimization to make reset simpler
+    (try-add-nine vi hi))
+
+  ; loop through nines but being able to add more flashes
+  (for ([j (in-naturals)] #:break (= j index))
+    (match-define (cons pv ph) (vector-ref nines j))
+
+    (define (touch-point pv ph)
+      (when (and (and (>= pv 0) (< pv v)) (and (>= ph 0) (< ph h)))
+        (try-add-nine pv ph)))
+
+    (for* ([dv (in-range -1 2)] [dh (in-range -1 2)] #:unless (= 0 dv dh))
+      (touch-point (+ pv dv) (+ ph dh))))
+
+  index)
+
+; part 1
+(for/sum ([i (in-range 100)])
+  (apply-step i))
+; part 2
+(for/last ([i (in-naturals)])
+  #:break (= (apply-step i) (* v h))
+  (+ i 100 2))

2021/day11/test1.txt

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+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526

2021/day11/test2.txt

@@ -0,0 +1,10 @@
+4721224663
+6875415276
+2742448428
+4878231556
+5684643743
+3553681866
+4788183625
+4255856532
+1415818775
+2326886125