From 5deb958ffa847588a0ada659f300252489192372 Mon Sep 17 00:00:00 2001
From: Dustin Swan <dustin@dustinswan.com>
Date: Sun, 12 Dec 2021 20:44:47 -0500
Subject: [PATCH] day12

---
 day12.rkt      | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 day12.test.txt |  7 +++++++
 day12.txt      | 26 ++++++++++++++++++++++++++
 3 files changed, 83 insertions(+)
 create mode 100644 day12.rkt
 create mode 100644 day12.test.txt
 create mode 100644 day12.txt

diff --git a/day12.rkt b/day12.rkt
new file mode 100644
index 0000000..a57bce3
--- /dev/null
+++ b/day12.rkt
@@ -0,0 +1,50 @@
+#lang racket
+
+(define connections
+  (map (λ (s) (string-split s "-"))
+       (file->lines "day12.txt")))
+
+(define (small-cave? cave)
+  (and (equal? (string-downcase cave) cave)
+       (not (equal? cave "start"))))
+
+(define (find-connections cns cave)
+  (filter (λ (x) (not (equal? "start" x)))
+          (append (map second (filter (λ (x) (equal? cave (first x))) cns))
+                  (map first (filter (λ (x) (equal? cave (second x))) cns)))))
+
+(define (go cns cave seent)
+  (define nexts (find-connections cns cave)) ; find every cave you can reach next from node
+  (define unvisited (filter (λ (x) (not (member x seent))) nexts)) ; filter out the caves we've seen't
+  (define new-seent (if (small-cave? cave) (cons cave seent) seent)) ; if it's a small cave, add it to the seen't list
+  (define paths (map (λ (x) (go cns x new-seent)) unvisited)) ; recurse over all of the connections
+  (cons cave (if (equal? "end" cave) ; if we've reach the end..
+                 '() ; don't go back up the tree
+                 paths)))
+
+(define part1
+  (let* ([tree (go connections "start" '())]
+         [flat (flatten tree)]
+         [ends (length (filter (λ (x) (equal? "end" x)) flat))])
+    ends))
+
+part1
+
+; PART 2
+
+(define (go2 cns cave seent revisitable)
+  (define nexts (find-connections cns cave)) ; find every cave you can reach next from node
+  (define new-seent (if (small-cave? cave) (cons cave seent) seent))
+  (if (equal? "end" cave)
+      1 ; add one when we get to the end
+      (foldl (λ (x acc) (+ acc (if (and (member x new-seent) revisitable) ; if it's a small cave, and we haven't revisited yet
+                                   (go2 cns x new-seent #f) ; recurse setting revisitable to #f
+                                   (if (not (member x seent)) ; otherwise, if we hadn't seen it yet
+                                       (go2 cns x new-seent revisitable) ; recurse
+                                       0)))) ; otherwise, it doesn't end. add 0
+             0 nexts)))
+
+(define part2
+  (go2 connections "start" '() #t))
+
+part2
\ No newline at end of file
diff --git a/day12.test.txt b/day12.test.txt
new file mode 100644
index 0000000..6fd8c41
--- /dev/null
+++ b/day12.test.txt
@@ -0,0 +1,7 @@
+start-A
+start-b
+A-c
+A-b
+b-d
+A-end
+b-end
diff --git a/day12.txt b/day12.txt
new file mode 100644
index 0000000..f60a240
--- /dev/null
+++ b/day12.txt
@@ -0,0 +1,26 @@
+CV-mk
+gm-IK
+sk-gm
+ca-sk
+sx-mk
+gm-start
+sx-ca
+kt-sk
+ca-VS
+kt-ml
+kt-ca
+mk-IK
+end-sx
+end-sk
+gy-sx
+end-ca
+ca-ml
+gm-CV
+sx-kt
+start-CV
+IK-start
+CV-kt
+ml-mk
+ml-CV
+ml-gm
+ml-IK