Data commit

Task/Lah-numbers/Haskell/lah-numbers.hs

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+import Text.Printf (printf)
+import Control.Monad (when)
+
+factorial :: Integral n => n -> n
+factorial 0 = 1
+factorial n = product [1..n]
+
+lah :: Integral n => n -> n -> n
+lah n k
+  | k == 1 = factorial n
+  | k == n = 1
+  | k > n  = 0
+  | k < 1 || n < 1 = 0
+  | otherwise = f n `div` f k `div` factorial (n - k)
+      where
+        f = (*) =<< (^ 2) . factorial . pred
+
+printLah :: (Word, Word) -> IO ()
+printLah (n, k) = do
+  when (k == 0) (printf "\n%3d" n)
+  printf "%11d" (lah n k)
+
+main :: IO ()
+main = do
+  printf "Unsigned Lah numbers: L(n, k):\nn/k"
+  mapM_ (printf "%11d") zeroToTwelve
+  mapM_ printLah $ (,) <$> zeroToTwelve <*> zeroToTwelve
+  printf "\nMaximum value from the L(100, *) row:\n%d\n"
+    (maximum $ lah 100 <$> ([0..100] :: [Integer]))
+  where zeroToTwelve = [0..12]