Day 4

app/Main.hs

@@ -3,6 +3,7 @@ module Main where
 import Day1
 import Day2
 import Day3
+import Day4
 import System.IO
 import Data.List.Split
 import Data.Set
@@ -41,4 +42,8 @@ main = do
     r_day3 <- readFile "./app/input_day3"
     putStr "[Day 3] Result: "
     print $ getDistanceAndSteps r_day3
+    putStr "[Day 4-1] Result: "
+    print getNumberOfPasswords
+    putStr "[Day 4-2] Result: "
+    print getNumberOfPasswords'
 

src/Day4.hs

@@ -0,0 +1,29 @@
+module Day4
+    (
+      getNumberOfPasswords
+    , getNumberOfPasswords'
+    ) where
+
+import Data.List
+
+generatePasswords_Part1 :: [Integer]
+generatePasswords_Part1 =
+    [ x | x <- [145852..616942]
+        , has2Same (show x)
+        , increases ((read :: String -> Integer) . (:[]) <$> show x)]
+    where
+        has2Same xs = let ys = zip xs (tail xs ++ " ") in
+            any (uncurry (==)) ys
+        increases [] = True
+        increases xs = let ys = zip xs (tail xs ++ [maximum xs]) in
+            all (uncurry (<=)) ys
+
+getNumberOfPasswords :: Int
+getNumberOfPasswords = length generatePasswords_Part1
+
+generatePasswords_Part2 :: [Integer]
+generatePasswords_Part2 = filter f generatePasswords_Part1
+    where f x = 2 `elem` (length <$> group (show x))
+
+getNumberOfPasswords' :: Int
+getNumberOfPasswords' = length generatePasswords_Part2