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hello-algo/en/codes/java/chapter_greedy/fractional_knapsack.java

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/**
* File: fractional_knapsack.java
* Created Time: 2023-07-20
* Author: krahets (krahets@163.com)
*/
package chapter_greedy;
import java.util.Arrays;
import java.util.Comparator;
/* Item */
class Item {
int w; // Item weight
int v; // Item value
public Item(int w, int v) {
this.w = w;
this.v = v;
}
}
public class fractional_knapsack {
/* Fractional knapsack: Greedy */
static double fractionalKnapsack(int[] wgt, int[] val, int cap) {
// Create an item list, containing two properties: weight, value
Item[] items = new Item[wgt.length];
for (int i = 0; i < wgt.length; i++) {
items[i] = new Item(wgt[i], val[i]);
}
// Sort by unit value item.v / item.w from high to low
Arrays.sort(items, Comparator.comparingDouble(item -> -((double) item.v / item.w)));
// Loop for greedy selection
double res = 0;
for (Item 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;
}
public static void main(String[] args) {
int[] wgt = { 10, 20, 30, 40, 50 };
int[] val = { 50, 120, 150, 210, 240 };
int cap = 50;
// Greedy algorithm
double res = fractionalKnapsack(wgt, val, cap);
System.out.println("The maximum value within the bag capacity is " + res);
}
}