feat: solve part 2 of day 2

app/Day2.hs

@@ -1,13 +1,13 @@
 module Main where
 
+import Debug.Trace
 import System.Environment (getArgs)
 
 main :: IO ()
 main = do
   input <- readFile . head =<< getArgs
   print $ part1 input
-
--- print $ part2 input
+  print $ part2 input
 
 part1 :: String -> Int
 part1 = sum . filter invalid . concat . map ids . map parse . splitOn ','
@@ -36,4 +36,21 @@ invalid i =
       half = take (len `div` 2) s
    in s == half ++ half
 
+part2 :: String -> Int
+part2 = sum . filter invalid2 . concat . map ids . map parse . splitOn ','
+
+invalid2 :: Int -> Bool
+invalid2 i =
+  let s = show i
+      len = length s
+      facs = factors len
+   in or [(repeatN (len `div` n) $ take n s) == s | n <- facs]
+
+-- needs to get the primes instead of all factors
+factors :: Int -> [Int]
+factors i = filter ((== 0) . (mod i)) [1 .. i `div` 2]
+
+repeatN :: Int -> [a] -> [a]
+repeatN i = concat . replicate i
+
 testInput = "11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124"