Data commit

Task/Eban-numbers/Haskell/eban-numbers.hs

@@ -0,0 +1,33 @@
+{-# LANGUAGE NumericUnderscores #-}
+import Data.List (intercalate)
+import Text.Printf (printf)
+import Data.List.Split (chunksOf)
+
+isEban :: Int -> Bool
+isEban n = all (`elem` [0, 2, 4, 6]) z
+ where
+  (b, r1) = n  `quotRem` (10 ^ 9)
+  (m, r2) = r1 `quotRem` (10 ^ 6)
+  (t, r3) = r2 `quotRem` (10 ^ 3)
+  z       = b : map (\x -> if x >= 30 && x <= 66 then x `mod` 10 else x) [m, t, r3]
+
+ebans = map f
+ where
+  f x = (thousands x, thousands $ length $ filter isEban [1..x])
+
+thousands:: Int -> String
+thousands = reverse . intercalate "," . chunksOf 3 . reverse . show
+
+main :: IO ()
+main = do
+  uncurry (printf "eban numbers up to and including 1000: %2s\n%s\n\n") $ r [1..1000]
+  uncurry (printf "eban numbers between 1000 and 4000: %2s\n%s\n\n") $ r [1000..4000]
+  mapM_ (uncurry (printf "eban numbers up and including %13s: %5s\n")) ebanCounts
+ where
+  ebanCounts = ebans [        10_000
+                     ,       100_000
+                     ,     1_000_000
+                     ,    10_000_000
+                     ,   100_000_000
+                     , 1_000_000_000 ]
+  r = ((,) <$> thousands . length <*> show) . filter isEban