From 96feb113538b18d615b02fc5886dd66abfd79d19 Mon Sep 17 00:00:00 2001
From: Jan Tuomi <jans.tuomi@gmail.com>
Date: Sun, 12 Dec 2021 14:19:55 +0200
Subject: Day 12

---
 day12/input.txt |  24 +++++++++++++
 day12/main.hs   | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 day12/test.txt  |   7 ++++
 day12/test2.txt |  10 ++++++
 day12/test3.txt |  18 ++++++++++
 5 files changed, 161 insertions(+)
 create mode 100644 day12/input.txt
 create mode 100644 day12/main.hs
 create mode 100644 day12/test.txt
 create mode 100644 day12/test2.txt
 create mode 100644 day12/test3.txt

diff --git a/day12/input.txt b/day12/input.txt
new file mode 100644
index 0000000..74dcdd2
--- /dev/null
+++ b/day12/input.txt
@@ -0,0 +1,24 @@
+hl-WP
+vl-fo
+vl-WW
+WP-start
+vl-QW
+fo-wy
+WW-dz
+dz-hl
+fo-end
+VH-fo
+ps-vl
+FN-dz
+WP-ps
+ps-start
+WW-hl
+end-QW
+start-vl
+WP-fo
+end-FN
+hl-QW
+WP-dz
+QW-fo
+QW-dz
+ps-dz
diff --git a/day12/main.hs b/day12/main.hs
new file mode 100644
index 0000000..50402e6
--- /dev/null
+++ b/day12/main.hs
@@ -0,0 +1,102 @@
+module Main where
+
+import Data.Char (isLower, isUpper)
+import Data.Function (on)
+import Data.List (concatMap, groupBy, intercalate, nub, sort, sortOn)
+import Data.Map.Strict (Map, (!))
+import qualified Data.Map.Strict as Map
+import Data.Text (pack, split, unpack)
+import Debug.Trace (traceShow)
+import Utils
+
+newtype Cave = Cave String
+
+instance Eq Cave where
+  (==) (Cave a) (Cave b) = a == b
+
+instance Ord Cave where
+  compare (Cave a) (Cave b) = compare a b
+
+instance Show Cave where
+  show (Cave cave) = show cave
+
+newtype Graph = Graph (Map Cave [Cave])
+
+instance Show Graph where
+  show (Graph hmap) = show hmap
+
+newtype Path = Path [Cave]
+
+instance Show Path where
+  show (Path caves) = caves $> map (\(Cave s) -> s) .> intercalate ","
+
+neighbors (Graph hmap) c = hmap ! c
+
+groupCavePairs :: [(String, String)] -> [(Cave, [Cave])]
+groupCavePairs =
+  sortOn fst
+    .> groupBy ((==) `on` fst)
+    .> map (\lst -> (Cave $ fst (head lst), map (snd .> Cave) lst))
+
+toPair [a, b] = (a, b)
+toPair other = error $ "invalid list: " ++ show other
+
+flipPair (a, b) = (b, a)
+
+isSmall (Cave cave) = isLower (head cave)
+
+isBig (Cave cave) = isUpper (head cave)
+
+isStart (Cave cave) = cave == "start"
+
+isEnd (Cave cave) = cave == "end"
+
+walk1 :: Graph -> Path -> Cave -> [Path]
+walk1 graph (Path path) c
+  | isEnd c = [Path $ reverse (c : path)]
+  | c `elem` path && isSmall c = []
+  | otherwise =
+    let path' = Path $ c : path
+        ns = neighbors graph c
+     in concatMap (walk1 graph path') ns
+
+e1 :: Graph -> [Path]
+e1 graph = walk1 graph (Path []) (Cave "start")
+
+countBy f = filter f .> length
+
+count lst el = filter (== el) lst $> length
+
+walk2 :: Graph -> Path -> Bool -> Cave -> Int
+walk2 graph p@(Path path) smallVisitedTwice c@(Cave cName)
+  | isEnd c = 1
+  | isStart c && c `elem` path = 0
+  | isSmall c && c `elem` path && smallVisitedTwice = 0
+  | isSmall c && c `elem` path && not smallVisitedTwice =
+    let path' = Path $ c : path
+        ns = neighbors graph c
+     in sum $ map (walk2 graph path' True) ns
+  | otherwise =
+    let path' = Path $ c : path
+        ns = neighbors graph c
+     in sum $ map (walk2 graph path' smallVisitedTwice) ns
+
+e2 graph = walk2 graph (Path []) False (Cave "start")
+
+main :: IO ()
+main =
+  do
+    contents <- getContents
+
+    let input =
+          contents
+            $> lines
+            .> map (pack .> split (== '-') .> map unpack .> toPair)
+            .> concatMap (\p -> [p, flipPair p])
+
+    let graph = Graph $ Map.fromList $ groupCavePairs input
+
+    let result1 = e1 graph
+    result1 $> length .> print
+    let result2 = e2 graph
+    result2 $> print
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/test2.txt b/day12/test2.txt
new file mode 100644
index 0000000..62cc714
--- /dev/null
+++ b/day12/test2.txt
@@ -0,0 +1,10 @@
+dc-end
+HN-start
+start-kj
+dc-start
+dc-HN
+LN-dc
+HN-end
+kj-sa
+kj-HN
+kj-dc
diff --git a/day12/test3.txt b/day12/test3.txt
new file mode 100644
index 0000000..65f3833
--- /dev/null
+++ b/day12/test3.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
-- 
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