Initial data commit

Task/Matrix-chain-multiplication/Haskell/matrix-chain-multiplication.hs

@@ -0,0 +1,41 @@
+import Data.List (elemIndex)
+import Data.Char (chr, ord)
+import Data.Maybe (fromJust)
+
+mats :: [[Int]]
+mats =
+  [ [5, 6, 3, 1]
+  , [1, 5, 25, 30, 100, 70, 2, 1, 100, 250, 1, 1000, 2]
+  , [1000, 1, 500, 12, 1, 700, 2500, 3, 2, 5, 14, 10]
+  ]
+
+cost :: [Int] -> Int -> Int -> (Int, Int)
+cost a i j
+  | i < j =
+    let m =
+          [ fst (cost a i k) + fst (cost a (k + 1) j) +
+           (a !! i) * (a !! (j + 1)) * (a !! (k + 1))
+          | k <- [i .. j - 1] ]
+        mm = minimum m
+    in (mm, fromJust (elemIndex mm m) + i)
+  | otherwise = (0, -1)
+
+optimalOrder :: [Int] -> Int -> Int -> String
+optimalOrder a i j
+  | i < j =
+    let c = cost a i j
+    in "(" ++ optimalOrder a i (snd c) ++ optimalOrder a (snd c + 1) j ++ ")"
+  | otherwise = [chr ((+ i) $ ord 'a')]
+
+printBlock :: [Int] -> IO ()
+printBlock v =
+  let c = cost v 0 (length v - 2)
+  in putStrLn
+       ("for " ++
+        show v ++
+        " we have " ++
+        show (fst c) ++
+        " possibilities, z.B " ++ optimalOrder v 0 (length v - 2))
+
+main :: IO ()
+main = mapM_ printBlock mats