haskell: add [p12, p17]

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

haskell/p14.hs

@@ -0,0 +1,15 @@
+import Data.Ord (comparing)
+import Data.List (maximumBy)
+
+main :: IO ()
+main = putStr $ show $ fst $ maximumBy (comparing snd) $ zip range $ map collatz range
+  where
+    range :: [ Int ]
+    range = [1 .. 10 ^ 6 - 1]
+
+-- eh 12s isn't much
+collatz :: Int -> Int
+collatz n
+  | n == 1 = 1
+  | even n = 1 + collatz (div n 2)
+  | otherwise = 1 + collatz (3 * n + 1)