Started to implement Knapsack.

discrete_optimization.sublime-project

@@ -1,4 +1,13 @@
 {
+	"build_systems":
+	[
+		{
+			"file_regex": "^[ ]*File \"(...*?)\", line ([0-9]*)",
+			"name": "Anaconda Python Builder",
+			"selector": "source.python",
+			"shell_cmd": "\"python\" -u \"$file\""
+		}
+	],
 	"folders":
 	[
 		{

knapsack/knapsack.py

@@ -62,8 +62,58 @@ def solve_knapsack_dynamic(knapsack):
 
 
 def solve_knapsack_depth_first_search(knapsack):
-    objective = 0
-    pass
+    knapsack.items.sort(key=lambda item: item.value / item.weight,
+                        reverse=True)
+    num_items = len(knapsack.items)
+    result = {"objective": 0,
+              "path": []}
+
+    def get_max_value(from_index, capacity):
+        value = 0
+        for item in knapsack.items[from_index:]:
+            if item.weight <= capacity:
+                value += item.value
+                capacity -= item.weight
+            else:
+                value += int((item.weight / capacity) * item.value) + 1
+                return value
+        return value
+
+        return sum([i.value for i in knapsack.items[from_index:]])
+
+    def search(index, capacity, value, path, result):
+
+        if capacity < 0:
+            return
+
+        if value > result["objective"]:
+            result["objective"] = value
+            result["path"] = path
+
+        # Take current item.
+        if value + get_max_value(index, capacity) > result["objective"]:
+            item = knapsack.items[index]
+            new_index = index + 1
+            new_path = path + [1]
+            new_capacity = capacity - item.weight
+            new_value = value + item.value
+            search(new_index, new_capacity, new_value, new_path, result)
+
+        # Do not take current item.
+        new_index = index + 1
+        if value + get_max_value(new_index, capacity) > result["objective"]:
+            new_path = path + [0]
+            search(new_index, capacity, value, new_path, result)
+
+    def correct_path(path):
+        path = path + [0] * (num_items - len(path))
+        values = zip(path, knapsack.items)
+        path = [v[0] for v in sorted(values, key=lambda value: value[1].index)]
+        return path
+
+    search(0, knapsack.capacity, 0, [], result)
+
+    return Result(result["objective"], 1, correct_path(result["path"]))
 
 
 def input_data_to_knapsack(input_data):
@@ -74,7 +124,7 @@ def input_data_to_knapsack(input_data):
     for i in range(1, item_count + 1):
         line = lines[i]
         value, weight = map(int, line.split())
-        items.append(Item(i-1, value, weight))
+        items.append(Item(i - 1, value, weight))
 
     k = Knapsack(item_count, capacity, items)
     return k
@@ -87,3 +137,10 @@ def result_to_output_data(result):
     return output_data
 
 
+if __name__ == '__main__':
+    file_location = "./data/ks_60_0"
+    with open(file_location, 'r') as input_data_file:
+        input_data = input_data_file.read()
+    k = input_data_to_knapsack(input_data)
+    print(result_to_output_data(solve_knapsack_dynamic(k)))
+    print(result_to_output_data(solve_knapsack_depth_first_search(k)))

knapsack/solver.py

@@ -25,4 +25,3 @@ if __name__ == '__main__':
         print("This test requires an input file.  "
               "Please select one from the data directory. "
               "(i.e. python solver.py ./data/ks_4_0)")
-