problem 32 haskell

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+------
+-- Pandigital products
+-- Problem 32
+--
+-- We shall say that an n-digit number is pandigital if it makes use of all the digits
+-- 1 to n exactly once; for example, the 5-digit number, 15234, is 1 through 5 pandigital.
+-- The product 7254 is unusual, as the identity, 39 × 186 = 7254, containing multiplicand,
+-- multiplier, and product is 1 through 9 pandigital.
+-- Find the sum of all products whose multiplicand/multiplier/product identity can
+-- be written as a 1 through 9 pandigital.
+-- HINT: Some products can be obtained in more than one way so be sure to only
+-- include it once in your sum.
+------
+
+
+import Data.List(sort, nubBy, nub)
+
+main = do
+    print (sum $ nub [a * b | a <- [1..2000], b <- [1..2000], isPandigitalProd a b])
+
+isPandigitalProd :: Int -> Int -> Bool
+isPandigitalProd a b = sort (revDigits a ++ revDigits b ++ revDigits (a * b)) == [1..9]
+
+revDigits :: Int -> [Int]
+revDigits 0 = []
+revDigits x = x `mod` 10 : revDigits (x `div` 10)