Data commit

Task/Lychrel-numbers/Haskell/lychrel-numbers.hs

@@ -0,0 +1,50 @@
+module Main where
+
+import Data.List
+
+procLychrel :: Integer -> [Integer]
+procLychrel a = a : pl a
+  where
+    pl n =
+        let s = n + reverseInteger n
+             in if isPalindrome s
+                  then [s]
+                  else s : pl s
+
+isPalindrome :: Integer -> Bool
+isPalindrome n =
+  let s = show n
+  in (s == reverse s)
+
+isLychrel :: Integer -> Bool
+isLychrel = not . null . drop 500 . procLychrel
+
+reverseInteger :: Integer -> Integer
+reverseInteger = read . reverse . show
+
+seedAndRelated :: (Int, [Integer], [Integer], Int)
+seedAndRelated =
+  let (seed, related, _) = foldl sar ([], [], []) [1 .. 10000]
+      lseed = length seed
+      lrelated = length related
+      totalCount = lseed + lrelated
+      pal = filter isPalindrome $ seed ++ related
+  in (totalCount, pal, seed, lrelated)
+  where
+    sar (seed, related, lych) x =
+      let s = procLychrel x
+          sIsLychrel = not . null . drop 500 $ s
+          (isIn, isOut) = partition (`elem` lych) . take 501 $ s
+          newLych = lych ++ isOut
+      in if sIsLychrel
+           then if null isIn -- seed lychrel number
+                  then (x : seed, related, newLych)
+                  else (seed, x : related, newLych) -- related lychrel number
+           else (seed, related, lych)
+
+main = do
+  let (totalCount, palindromicLychrel, lychrelSeeds, relatedCount) = seedAndRelated
+  putStrLn $ "[1..10,000] contains " ++ show totalCount ++ " Lychrel numbers."
+  putStrLn $ show palindromicLychrel ++ " are palindromic Lychrel numbers."
+  putStrLn $ show lychrelSeeds ++ " are Lychrel seeds."
+  putStrLn $ "There are " ++ show relatedCount ++ " related Lychrel numbers."