Java描述贪心算法解决背包问题

思路: 首先将物品根据性价比排好序在一个集合里,性价比=价格/重量...

然后根据性价比从大到小依次依次放入背包,如果没办法放入这个物品的全部,就放入一部分,如果可以放入全量物品,就放入全量物品。

Main.java的代码

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

/**
 * Created by HuLuo on 2016/2/16.
 */
public class Main
{
    //背包总质量
    private static double M = 20;

    //物品数量
    private static int number = 3;


    public static void main(String[] args)
    {
        MyObject myObject1 = new MyObject( 18, 25 );

        MyObject myObject2 = new MyObject( 15, 24 );

        MyObject myObject3 = new MyObject( 10, 15 );

        ArrayList<MyObject> myObjects = new ArrayList<MyObject>( number );

        myObject1.priceRatio = ( myObject1.price * 1.0 ) / ( myObject1.weight );

        myObject2.priceRatio = ( myObject2.price * 1.0 ) / ( myObject2.weight );

        myObject3.priceRatio = ( myObject3.price * 1.0 ) / ( myObject3.weight );


        myObjects.add( myObject1 );
        myObjects.add( myObject2 );
        myObjects.add( myObject3 );


        //根据物品的性价比将集合中的物品做一个排序 ,按照性价比从大到小排列
        Collections.sort( myObjects, new Comparator<MyObject>()
        {
            @Override
            public int compare(MyObject o1, MyObject o2)
            {
                if(o1.priceRatio > o2.priceRatio)
                {
                    return -1;
                }
                else
                    return 1;
            }

        } );

        MyObject temp = null;

        for(int i = 0; i < number && M > 0; i++)
        {
            temp = myObjects.get( i );

            if(M >= temp.weight)
            {
                M = M - temp.weight;

                temp.x = 1.0;
            }

            else
            {
                temp.x = ( M * 1.0 ) / temp.weight;

                M = M - ( temp.weight * temp.x );
            }
        }

        for(MyObject myObject : myObjects)
        {
            System.out.println( "物品价格是:" + myObject.price + "的物品, 装入比例是:" + myObject.x );
        }

    }
}

/**
 * Created by HuLuo on 2016/2/16.
 */

/**
 * 物品对象
 */
public class MyObject
{

    public int weight = 0;

    public int price = 0;

    //装入的比例
    public double x = 0;

    //性价比
    public double priceRatio = 0 ;

    public MyObject(int weight, int price)
    {
        this.weight = weight;

        this.price = price;
    }

}