src/projectEuler/question14.hs

@@ -16,24 +16,33 @@ NOTE: Once the chain starts the terms are allowed to go above one million.
 -}
 module Main where
 
-import           Data.List (sortOn)
-import           Data.Ord  (Down (Down))
+-- import           Data.Set    (Set)
+-- import qualified Data.Set    as Set
+
+import           Data.IntSet (IntSet)
+import qualified Data.IntSet as IntSet
 
 main :: IO ()
 main = print ans
 
-ans :: Int
-ans = fst $ head $ sortOn (Down . snd) $ map collatzChainStartingAt [1..limit]
+ans :: Integer
+ans = 42
 
-nextCollatz :: Int -> Int
 nextCollatz n
   | n == 1 = 0
   | even n = n `div` 2
   | odd  n = 3*n + 1
 
-collatzChainStartingAt :: Int -> (Int, Int)
-collatzChainStartingAt n = (n, s')
-  where s' = length $ takeWhile (/= 0) $ iterate nextCollatz n
+collatzChainStartingAt n = takeWhile (/= 0) $ iterate nextCollatz n
 
-limit :: Int
+-- solve limit = (n, chain)
+--   where
+--     s = maximum
+--       $ map length
+--       $ map collatzChainStartingAt [1..limit]
 limit = 1_000_000
+
+wholePositiveNumbers :: IntSet
+wholePositiveNumbers = IntSet.fromDistinctAscList [1..limit]
+
+f = IntSet.foldl (\acc key -> collatzChainStartingAt key : acc) []