2020 day 6

2020/day06/part1.hs

@@ -0,0 +1,28 @@
+import Data.List
+
+
+main :: IO ()
+main = do
+    input <- readFile "input"
+    print . sum . map length . groups $ input
+
+
+-- Collect each group's answers
+groups :: String -> [String]
+groups = map (foldr1 union . lines) . dlfsplit
+
+-- Split a string into a list across all the double newlines in it
+dlfsplit :: String -> [String]
+dlfsplit str = a : case b of
+        [] -> []
+        b -> dlfsplit b
+    where (a,b) = dlfsplitonce str
+
+-- Split a string into two across the first double newline found
+dlfsplitonce :: String -> (String, String)
+dlfsplitonce [] = ([], [])
+dlfsplitonce (ca:cb:rest)
+    | ca == '\n' && cb == '\n' = ([], rest)
+    | otherwise                = (ca:before, after)
+        where (before, after) = dlfsplitonce (cb : rest)
+dlfsplitonce c = (c, [])

2020/day06/part2.hs

@@ -0,0 +1,28 @@
+import Data.List
+
+
+main :: IO ()
+main = do
+    input <- readFile "input"
+    print . sum . map length . groups $ input
+
+
+-- Collect each group's answers
+groups :: String -> [String]
+groups = map (foldr1 intersect . lines) . dlfsplit
+
+-- Split a string into a list across all the double newlines in it
+dlfsplit :: String -> [String]
+dlfsplit str = a : case b of
+        [] -> []
+        b -> dlfsplit b
+    where (a,b) = dlfsplitonce str
+
+-- Split a string into two across the first double newline found
+dlfsplitonce :: String -> (String, String)
+dlfsplitonce [] = ([], [])
+dlfsplitonce (ca:cb:rest)
+    | ca == '\n' && cb == '\n' = ([], rest)
+    | otherwise                = (ca:before, after)
+        where (before, after) = dlfsplitonce (cb : rest)
+dlfsplitonce c = (c, [])