2016 Update

Task/Knapsack-problem-Continuous/Elixir/knapsack-problem-continuous-1.elixir

@@ -1,14 +1,16 @@
 defmodule KnapsackProblem do
-  def price_per_weight( items ), do: (for {name, weight, price} <-items, do: {name, weight, price / weight} )
-
   def select( max_weight, items ) do
-    {_remains, selected_items} = List.foldr( List.keysort(items, 2), {max_weight, []}, &select_until/2 )
-    selected_items
+    Enum.sort_by( items, fn {_name, weight, price} -> - price / weight end )
+    |> Enum.reduce( {max_weight, []}, &select_until/2 )
+    |> elem(1)
+    |> Enum.reverse
   end
 
-  def task( max_weight, items ) do
+  def task( items, max_weight ) do
     IO.puts "The robber takes the following to maximize the value"
-    for {name, weight} <- select( max_weight, price_per_weight(items) ), do: :io.fwrite("~.2f of ~s~n", [weight, name])
+    Enum.each( select( max_weight, items ), fn {name, weight} ->
+      :io.fwrite("~.2f of ~s~n", [weight, name])
+    end )
   end
 
   defp select_until( {name, weight, _price}, {remains, acc} ) when remains > 0 do
@@ -31,4 +33,4 @@ items = [ {"beef",    3.8, 36},
           {"salami",  3.0, 95},
           {"sausage", 5.9, 98} ]
 
-KnapsackProblem.task( 15, items )
+KnapsackProblem.task( items, 15 )

Task/Knapsack-problem-Continuous/Elixir/knapsack-problem-continuous-2.elixir

@@ -0,0 +1,32 @@
+defmodule KnapsackProblem do
+  def continuous(items, max_weight) do
+    Enum.sort_by(items, fn {_item, {weight, price}} -> -price / weight end)
+    |> Enum.reduce_while({max_weight,0}, fn {item, {weight, price}}, {rest, value} ->
+         if rest > weight do
+           IO.puts "Take all #{item}"
+           {:cont, {rest - weight, value + price}}
+         else
+           :io.format "Take ~.3fkg of ~s~n~n", [rest, item]
+           :io.format "Total value of swag is ~.2f~n", [value + rest*price/weight]
+           {:halt, :ok}
+         end
+       end)
+    |> case do
+         {weight, value} ->
+             :io.format "Total:  weight ~.3fkg, value ~p~n", [max_weight-weight, value]
+         x -> x
+       end
+  end
+end
+
+items = [ beef:    {3.8, 36},
+          pork:    {5.4, 43},
+          ham:     {3.6, 90},
+          greaves: {2.4, 45},
+          flitch:  {4.0, 30},
+          brawn:   {2.5, 56},
+          welt:    {3.7, 67},
+          salami:  {3.0, 95},
+          sausage: {5.9, 98} ]
+
+KnapsackProblem.continuous( items, 15 )