Add Advent 2021 - day 12.

2021/day11/p.rkt

@@ -0,0 +1,53 @@
+#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

@@ -0,0 +1,10 @@
+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

2021/day12/p.rkt

@@ -0,0 +1,43 @@
+#lang racket/base
+(require racket/string)
+(require racket/set)
+
+(define (cdrm l)
+  (car (cdr l)))
+
+(define (make-line t)
+  (sort (string-split t "-") string<?))
+
+(define sset (for/set ([t (in-lines)]) (make-line t)))
+
+(define caves (for/mutable-set ([s sset]) (car s)))
+(set-union! caves (for/set ([s sset]) (cdrm s)))
+(set-subtract! caves (set "start" "end"))
+
+(define (is-small s)
+  (char-lower-case? (string-ref s 0)))
+
+(define (valid-path p1 p2)
+  (set-member? sset (sort (list p1 p2) string<?)))
+
+(define (cannot-use-cave c used)
+  ;(hash-has-key? used c)) ; part 1
+  (and (hash-has-key? used c) (hash-has-key? used 0))) ; part 2
+
+(define (hash-handle! used c)
+  (hash-update! used c add1 0)
+  (when (= (hash-ref used c) 2)
+    (hash-set! used 0 #t)))
+
+(for/sum ([cave caves])
+  (define (recurse-path path used c)
+    (when (is-small c) (hash-handle! used c))
+    (set! path (append path (list c)))
+    (+ (if (valid-path "end" c) 1 0)
+       (for/sum ([nc caves]
+                 #:unless (or (equal? nc c) (cannot-use-cave nc used) (not (valid-path c nc))))
+         (recurse-path path (hash-copy used) nc))))
+
+  (if (valid-path "start" cave)
+      (recurse-path null (make-hash) cave)
+      0))

2021/day12/test1.txt

@@ -0,0 +1,7 @@
+start-A
+start-b
+A-c
+A-b
+b-d
+A-end
+b-end

2021/day12/test2.txt

@@ -0,0 +1,18 @@
+fs-end
+he-DX
+fs-he
+start-DX
+pj-DX
+end-zg
+zg-sl
+zg-pj
+pj-he
+RW-he
+fs-DX
+pj-RW
+zg-RW
+start-pj
+he-WI
+zg-he
+pj-fs
+start-RW

2021/day12/test3.txt

@@ -0,0 +1,22 @@
+end-MY
+MY-xc
+ho-NF
+start-ho
+NF-xc
+NF-yf
+end-yf
+xc-TP
+MY-qo
+yf-TP
+dc-NF
+dc-xc
+start-dc
+yf-MY
+MY-ho
+EM-uh
+xc-yf
+ho-dc
+uh-NF
+yf-ho
+end-uh
+start-NF