Add solution for problem 62.

Euler.hs

@@ -60,6 +60,8 @@ data Decimal = Decimal { integerPart     :: Integer
 whenM, unlessM :: Monad m => m Bool -> m () -> m ()
 whenM   mc m = mc >>= (\c -> when   c m)
 unlessM mc m = mc >>= (\c -> unless c m)
+{-# INLINE whenM   #-}
+{-# INLINE unlessM #-}
 
 primesTo n = LST.runST $ do
    isPrimeArr <- LST.strictToLazyST (newArray (2, n) 1 :: ST s (STUArray s Integer Word8))
@@ -98,6 +100,7 @@ primeFactors n = go n primes
 
 divides :: Integral a => a -> a -> Bool
 a `divides` b = b `mod` a == 0
+{-# INLINE divides #-}
 
 class Ix a => RangeIx a where
    intersectBounds :: (a, a) -> (a, a) -> (a, a)
@@ -152,6 +155,7 @@ instance Show Decimal where
 
 toDigits :: (Integral a, Integral b) => a -> [b]
 toDigits = toDigitsBase 10
+{-# INLINE toDigits #-}
 
 toDigitsBase :: (Integral a, Integral b) => a -> a -> [b]
 toDigitsBase n = reverse . unfoldr (\x ->
@@ -159,6 +163,7 @@ toDigitsBase n = reverse . unfoldr (\x ->
 
 fromDigits :: (Integral a, Integral b) => [a] -> b
 fromDigits = fromDigitsBase 10
+{-# INLINE fromDigits #-}
 
 fromDigitsBase :: (Integral a, Integral b) => b -> [a] -> b
 fromDigitsBase n = foldl' (\a b -> n * a + fromIntegral b) 0
@@ -170,6 +175,6 @@ isPalindrome xs = xs == reverse xs
 (\\\) :: Ord a => [a] -> [a] -> [a]
 (a:as) \\\ (b:bs) = case compare a b of
    LT -> a : (as \\\ (b:bs))
-   EQ ->      as \\\ (b:bs)
+   EQ ->      as   \\\   bs
    GT ->      (a:as) \\\ bs
 infix 5 \\\

Problem062.hs

@@ -0,0 +1,16 @@
+-- The cube, 41063625 (345^3), can be permuted to produce two other cubes:
+-- 56623104 (384^3) and 66430125 (405^3). In fact, 41063625 is the smallest
+-- cube which has exactly three permutations of its digits which are also cube.
+--
+-- Find the smallest cube for which exactly five permutations of its digits are
+-- cube.
+
+import Euler
+
+main = print $ head $ do
+   let cubes = map (^3) [1..]
+   x <- cubes
+   let ps = filter ((== sort (toDigits x)) . sort . toDigits)
+          $ takeWhile (< 10 * x) $ dropWhile (< x) cubes
+   guard $ length ps == 5
+   return x