Day 9, Part 2

Day9/puzzle2.hs

@@ -0,0 +1,61 @@
+import Data.List (intersperse, groupBy)
+import Data.Char (digitToInt)
+import Data.Maybe (fromMaybe)
+import Data.Function (on)
+import qualified Data.Sequence as S
+import qualified Data.Foldable as F
+
+type DiskElem = (Int, Int)
+
+parseDiskMap :: [Int] -> S.Seq DiskElem
+parseDiskMap xs = let values = intersperse (-1) [0..]
+                  in  S.fromList $ zip values xs
+
+isSpaceEnough :: Int -> DiskElem -> Bool
+isSpaceEnough n (-1, l) = l >= n
+isSpaceEnough _ _ = False
+
+updateSpace :: Int -> DiskElem -> DiskElem
+updateSpace n (-1, l) = (-1, l - n)
+
+combineSpace :: DiskElem -> DiskElem -> DiskElem
+combineSpace (-1, l1) (-1, l2) = (-1, l1 + l2)
+
+compareFileValue :: Int -> DiskElem -> Bool
+compareFileValue x (v, _) = x == v
+
+moveFile :: Int -> Int -> DiskElem -> DiskElem -> S.Seq DiskElem -> S.Seq DiskElem
+moveFile i sIndex sVal fVal xs = let xs' = F.toList . S.insertAt sIndex fVal . S.insertAt sIndex sVal . S.deleteAt sIndex . S.insertAt i (-1, snd fVal) $ S.deleteAt i xs
+                                 in  S.fromList $ map (foldl1 combineSpace) $ groupBy ((==) `on` fst) xs'
+
+compactFiles :: Int -> S.Seq DiskElem -> S.Seq DiskElem
+compactFiles (-1) xs = xs
+compactFiles 0 xs = xs
+compactFiles n xs = if fst fVal == -1 || sIndex == -1 || sIndex >= n
+                        then compactFiles (n - 1) xs
+                    else compactFiles fIndex xs'
+                        where fVal   = S.index xs n
+                              sIndex = fromMaybe (-1) $ S.findIndexL (isSpaceEnough (snd fVal)) xs
+                              sVal   = updateSpace (snd fVal) (fromMaybe (-1, 0) $ S.lookup sIndex xs)
+                              xs'    = moveFile n sIndex sVal fVal xs
+                              fIndex = fromMaybe (-1) $ S.findIndexR (compareFileValue (fst fVal - 1)) xs'
+
+maskMinus1 :: [Int] -> [Int]
+maskMinus1 [] = []
+maskMinus1 (l:ls)
+    | l == -1   = 0:maskMinus1 ls
+    | otherwise = l:maskMinus1 ls
+
+tuplesToIntList :: S.Seq DiskElem -> [Int]
+tuplesToIntList disk = let listDisk = F.toList disk
+                       in  concatMap (\x -> replicate (snd x) (fst x)) listDisk
+
+checksum :: [Int] -> Int
+checksum xs = sum $ zipWith (*) (maskMinus1 xs) [0..]
+
+main = do
+    contents <- init <$> readFile "day9.txt"
+    let disk = parseDiskMap $ map digitToInt contents
+        i = fromMaybe (-1) $ S.findIndexR (\x -> fst x /= -1) disk
+        compactedDisk = tuplesToIntList $ S.filter (\x -> snd x > 0) $ compactFiles i disk
+    print $ checksum compactedDisk