reorg and add code for second edition

11_dynamic_programming/Haskell/01_knapsack-powerset.hs

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+import Control.Applicative
+import Data.List
+import qualified Data.Set as Set
+import qualified Data.HashMap.Strict as Map
+
+items = Map.fromList [
+  ("stereo", (4, 3000)),
+  ("laptop", (3, 2000)),
+  ("guitar", (1, 1500))
+  ]
+
+value set = (a, b)
+  where
+    weightandvalues = (sequence $ map (`Map.lookup`  items) set)
+    Just (a,b) = Just (foldl (\(a,b) (c,d) -> (a+c, b+d)) (0,0)) <*> weightandvalues
+
+powerSet xs = foldl (\acc x -> acc ++ (map (\e -> x:e) acc)) [[]] xs
+
+solution = foldl
+  (\acc v -> let
+      (firstweight, firstvalue) = value acc
+      (secondweight, secondvalue) = value v
+    in if firstweight <= 4 && firstvalue >= secondvalue then acc else if secondweight <= 4 then v else acc)
+  first
+  rest
+  where
+    (first: rest) = filter (not . null) $ powerSet $ (Map.keys items)

11_dynamic_programming/Haskell/01_knapsack_dynamic_prog.hs

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+import qualified Data.HashMap.Strict as Map
+import Data.Array
+
+type Grid = Array (Integer, Integer) (Integer, [Char])
+
+itemsMap = Map.fromList [
+  ("stereo", (4, 3000)),
+  ("laptop", (3, 2000)),
+  ("guitar", (1, 1500)),
+  ("iphone", (1, 2000))
+  ]
+
+weightOf item = case Map.lookup item itemsMap of
+  Just (w, v) -> w
+  otherwise -> 0
+
+valueOf item = case Map.lookup item itemsMap of
+  Just (w, v) -> v
+  otherwise -> 0
+
+emptyGrid :: Grid
+emptyGrid = array ((0,0), (3,4)) [((x,y), (0, "")) | x <- [0..3], y <- [0..4]]
+
+best :: Grid -> Integer -> Integer -> String -> (Integer, String)
+best arr row col item =
+  let weight = weightOf item
+      value = valueOf item
+      (previousMax, previousItems) = if (row /= 0) then arr ! (row - 1, col) else  (0, "")
+      (valueOfRemainingSpace, itemsInRemainingSpace) =
+        if (row /= 0 && (col - weight) >= 0)
+        then arr ! (row - 1, col - weight)
+        else (0, "")
+  in if (previousMax > (value + valueOfRemainingSpace))
+     then arr ! (row - 1, col)
+     else (value + valueOfRemainingSpace, itemsInRemainingSpace ++ " " ++ item)
+
+fillPrevBest arr row col =
+  if row /= 0 then (//) arr [((row, col), arr ! (row - 1, col))] else arr
+
+fillGrid emptyGrid = foldl
+  (\acc pair ->
+    let row = fst pair
+        item = snd pair
+        (weight, value) = (weightOf item, valueOf item)
+    in  foldl
+        (\arr col ->
+          case weight <= col of
+            True -> (//) arr [((row, col), best arr row col item)]
+            False -> fillPrevBest arr row col
+        )
+        acc
+        [0..4]
+    )
+  emptyGrid
+  items
+  where items = zip [0..3] $ Map.keys itemsMap
+
+solution = foldl
+  (\(x, a) (y, b) -> if x > y then (x, a) else (y, b))
+  first
+  rest
+  where (first: rest) = elems $ fillGrid emptyGrid