From 1006f83446472f938a6475148cabacbd4a2adaf2 Mon Sep 17 00:00:00 2001
From: Xiretza <xiretza@xiretza.xyz>
Date: Sat, 5 Dec 2020 10:21:57 +0100
Subject: [PATCH] 2020 day5/haskell: add solution

---
 2020/day5/day5.hs | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 2020/day5/day5.hs

diff --git a/2020/day5/day5.hs b/2020/day5/day5.hs
new file mode 100644
index 0000000..2aa5dd2
--- /dev/null
+++ b/2020/day5/day5.hs
@@ -0,0 +1,23 @@
+import AoC
+
+import Data.List (sort)
+import Data.Maybe (fromJust)
+import Numeric (readInt)
+import Text.ParserCombinators.ReadP
+
+binarify :: String -> Maybe Int
+binarify = oneCompleteResult . readS_to_P $ readInt 2 (`elem` "BFLR") digitValue
+    where digitValue 'F' = 0
+          digitValue 'B' = 1
+          digitValue 'L' = 0
+          digitValue 'R' = 1
+
+findHole :: (Enum a, Eq a) => [a] -> Maybe a
+findHole (x:y:ys) | y == next = findHole $ y:ys
+                  | otherwise = Just next
+                  where next = succ x
+findHole _ = Nothing
+
+main = runAoC (fmap (fromJust . binarify) <$> lines) part1 part2
+    where part1 = foldr1 max
+          part2 = fromJust . findHole . sort