Project Euler #4

src/projectEuler/question4.hs

@@ -0,0 +1,21 @@
+-- https://projecteuler.net/problem=4
+
+import           Debug.Trace (trace)
+
+twoDigitProducts :: [Integer]
+twoDigitProducts = [ n*m | n <- [10..99], m <- [n..99] ]
+
+isPalindrome :: Integer -> Bool
+isPalindrome n = all (== True) $ zipWith (==) half half'
+  where
+    (half, half'') = splitAt h n'
+    half' = reverse half''
+    h  = length n' `div` 2
+    n' = show n
+    -- n' = trace (show n) $ show n
+
+solve :: Integer
+solve = maximum $ filter isPalindrome twoDigitProducts
+
+main :: IO ()
+main = print solve