build

en/docs/chapter_greedy/fractional_knapsack_problem.md

@@ -73,9 +73,41 @@ We have created an `Item` class in order to sort the items by their unit value.
 === "C++"
 
     ```cpp title="fractional_knapsack.cpp"
-    [class]{Item}-[func]{}
+    /* Item */
+    class Item {
+      public:
+        int w; // Item weight
+        int v; // Item value
 
-    [class]{}-[func]{fractionalKnapsack}
+        Item(int w, int v) : w(w), v(v) {
+        }
+    };
+
+    /* Fractional knapsack: Greedy */
+    double fractionalKnapsack(vector<int> &wgt, vector<int> &val, int cap) {
+        // Create an item list, containing two properties: weight, value
+        vector<Item> items;
+        for (int i = 0; i < wgt.size(); i++) {
+            items.push_back(Item(wgt[i], val[i]));
+        }
+        // Sort by unit value item.v / item.w from high to low
+        sort(items.begin(), items.end(), [](Item &a, Item &b) { return (double)a.v / a.w > (double)b.v / b.w; });
+        // Loop for greedy selection
+        double res = 0;
+        for (auto &item : items) {
+            if (item.w <= cap) {
+                // If the remaining capacity is sufficient, put the entire item into the knapsack
+                res += item.v;
+                cap -= item.w;
+            } else {
+                // If the remaining capacity is insufficient, put part of the item into the knapsack
+                res += (double)item.v / item.w * cap;
+                // No remaining capacity left, thus break the loop
+                break;
+            }
+        }
+        return res;
+    }
     ```
 
 === "Java"