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 );
}

}
}

MyObject.java文件的代码

/**
* 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;
}

}