Add 2019 day 4

y2019/src/Day4.hs

@@ -0,0 +1,32 @@
+module Day4 (day4) where
+
+import Data.List.Split
+import Data.List
+
+isValid :: (Int -> Bool) -> Int -> Bool
+isValid groupsCriteria n = length6 && isSorted && hasGroups
+  where digits = show n
+        length6 = (length digits) == 6
+        isSorted = digits == sort digits
+        hasGroups = any (\d -> groupsCriteria (length d)) (group digits)
+
+getNext :: (Int -> Bool) -> Int -> Int
+getNext groupsCriteria cur
+  | isValid groupsCriteria (cur + 1) = (cur + 1)
+  | otherwise = getNext groupsCriteria (cur + 1)
+
+day4 :: IO ()
+day4 = do
+  putStrLn "AoC 2019 day 4"
+  putStr "Enter input >"
+  input <- getLine
+  putStrLn ""
+
+  let range = (map read (splitOn "-" input)) :: [Int]
+  putStrLn ("Range is " ++ show (range !! 0) ++ " to " ++ show (range !! 1))
+
+  let iterP1 = takeWhile (< (range !! 1)) (iterate (getNext (> 1)) (range !! 0))
+  putStrLn ("Part1: " ++ show ((length iterP1) - 1))
+
+  let iterP2 = takeWhile (< (range !! 1)) (iterate (getNext (== 2)) (range !! 0))
+  putStrLn ("Part2: " ++ show ((length iterP2) - 1))