Haskell 001

haskell/e001.hs

@@ -0,0 +1,20 @@
+{- Add all the natural numbers below one thousand that are multiples of 3 or 5.
+
+    If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
+    Find the sum of all the multiples of 3 or 5 below 1000.
+-}
+
+import Text.Printf
+
+multiples :: (Integral a) => a -> a
+multiples max =
+    if max < 3 then
+        0
+    else
+        if (max `mod` 5 == 0 || max `mod` 3 == 0) then
+            max + multiples (max - 1)
+        else multiples (max - 1)
+
+main = do
+    printf "Sum of multiples below 10: %d\n" (multiples 9 :: Int)
+    printf "Sum of multiples below 1000: %d\n" (multiples 999 :: Int)