Added Haskell example for Dijkstras algorithm (#18)

* Adding binary search example for Haskell

* Adding selection sort example in Haskell

* Adding Haskell examples for chapter 3

* Adding examples for chapter 4

* Adding examples for chapter 5

* Adding git ignore

* Add Haskell example for BFS

* resetting

* Adding haskell example for dijkstras algorithm

* Adding Haskell example for chapter 8

* Adding power set based solution for set covering problem

* Adding Haskell examples for chap 9

09_dynamic_programming/Haskell/01_knapsack-powerset.hs

@@ -0,0 +1,27 @@
+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)