Cass Lamendola

.gitignore

@@ -57,3 +57,4 @@ typings/
 # dotenv environment variables file
 .env
 
+.vscode/

knapsack.py

@@ -5,9 +5,70 @@
 
 Item = namedtuple('Item', ['index', 'size', 'value'])
 
-def knapsack_solver(items, capacity):
-  # !!!! IMPLEMENT ME
-  pass
+def knapsack_solver_recursive(items, capacity):
+  def naive(items, capacity, sack, value):
+    item = items[0] if len(items) > 0 else None
+    if len(items) == 0:
+      return (sack, value)
+    elif len(items) == 1:
+      if item.size <= capacity:
+        sack.add(item.index)
+        value += item.value
+        return(sack, value, capacity-item.size)
+      else:
+        return (sack, value, capacity)
+    elif item.size <= capacity:
+      temp_sack = set(sack)
+      temp_sack.add(item.index)
+
+      leave = naive(items[1:], capacity, sack, value)
+      keep = naive(items[1:], capacity-item.size, temp_sack, value+item.value)
+      return max(leave, keep, key=lambda x: x[1])
+    else:
+      return naive(items[1:], capacity, sack, value)
+  result = naive(items, capacity, set(), 0)
+  return "Value: %s\nSize: %s\nChosen: %s" %(result[1], capacity-result[2], result[0])
+
+def knapsack_solver_greedy(items, capacity):
+  knapsack, total_cost, total_value = [], 0, 0
+  while capacity > 0:
+    biggest_gain, cost, value, chosen_item = -1, 0, 0, None
+    for item in items:
+      ratio = item.value/item.size
+      if item.size <= capacity and ratio > biggest_gain:
+        biggest_gain = ratio
+        chosen_item = item
+        value = item.value
+        cost = item.size
+    if chosen_item == None:
+      capacity = 0
+      break
+    else:
+      knapsack.append(chosen_item.index)
+      total_cost += cost
+      total_value += value
+      items.remove(chosen_item)
+      capacity -= cost
+  return "Value: %s\nSize: %s\nChosen: %s" %(total_value, total_cost, knapsack)
+
+def knapsack_solver_greedy_2(items, capacity):
+  remaining = capacity
+  knapsack, total = [], 0 
+  GreedyItem = namedtuple('GreedyItem',Item._fields+('ratio',))
+  new_items = []
+  for item in items:
+    new_item = GreedyItem(item.index, item.size, item.value, item.value/item.size)
+    new_items.append(new_item)
+  new_items.sort(key=lambda item: item[3], reverse=True)
+  for item in new_items:
+    if item.size <= remaining:
+      remaining -= item.size
+      knapsack.append(item.index)
+      total += item.value
+    else:
+      pass
+  return "Value: %s\nSize: %s\nChosen: %s" %(total, capacity-remaining, knapsack)
+
 
 if __name__ == '__main__':
   if len(sys.argv) > 1:
@@ -21,6 +82,6 @@ def knapsack_solver(items, capacity):
       items.append(Item(int(data[0]), int(data[1]), int(data[2])))
 
     file_contents.close()
-    print(knapsack_solver(items, capacity))
+    print(knapsack_solver_greedy_2(items, capacity))
   else:
     print('Usage: knapsack.py [filename] [capacity]')