11-1

1 files changed, 37 insertions, 0 deletions

diff --git a/11-1.hs b/11-1.hs
new file mode 100644
index 0000000..de60536
--- /dev/null
+++ b/11-1.hs
@@ -0,0 +1,37 @@
+data Tree = Node Int | Branch [Tree]
+
+toList :: Tree -> [Int]
+toList (Node n) = [n]
+toList (Branch ts) = concatMap toList ts
+
+digits :: Int -> Int
+digits n = floor $ logBase 10 (fromIntegral n) + 1
+
+transform :: Tree -> Tree
+transform (Node 0) = Node 1
+transform (Node n)
+  | even (digits n)   = Branch . map Node $ halves n
+  | otherwise         = Node $ n * 2024
+transform (Branch ts) = Branch $ fmap transform ts
+
+halves :: Int -> [Int]
+halves n = [ floor $ fromIntegral n / 10^x
+           , n `mod` 10^x
+           ]
+  where
+    x = digits n `div` 2
+
+parse :: String -> Tree
+parse = Branch . map (Node . read) . words
+
+flatten :: Tree -> Tree
+flatten = Branch . map Node . toList
+
+main :: IO ()
+main = getLine
+  >>= print
+  . length
+  . toList
+  . (!!25)
+  . iterate (flatten . transform)
+  . parse