贪心算法之01背包问题

贪心算法Q3——01背包问题

/*
问题描述：
有n件物品，每个物品都有一个大小和价值，给你一个固定容量的背包，要求装的东西价值总和最大
实例：
现在有重量分别为35 30 60 50 40 10 25，价值分别为10 40 30 50 35 40 30的物品，
背包最大承重为150，求该背包所能放置的物品最大价值是多少？
*
*/

package 贪心;

public class Article {
	public int weight,value;
	public double valueOfDensity;
	Article(int weight,int value){
		this.weight=weight;
		this.value=value;
		this.valueOfDensity=value*1.0/weight;
	}
	@Override
	public String toString() {
		return "Article [weight=" + weight + ", value=" + value + ", valueOfDensity=" + valueOfDensity + "]";
	}
}

package 贪心;


import java.util.Arrays;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;

public class _01背包问题 {
	//传一个比较器Comparator<Article> cmp 按设定关键字排序
	static void select(String title,Comparator<Article> cmp) {
		//将物品变量直接封装在成员方法里作为局部变量 就可以不用通过mian方法传参了
		Article [] articles=new Article[] {
				new Article(35,10),new Article(30,40),
				new Article(60,30),new Article(50,50),
				new Article(40,35),new Article(10,40),
				new Article(25,30)
		};
		Arrays.sort(articles, cmp);
		//将Article类封装到list存储结构
		List<Article> selectedArticles=new LinkedList<>();
		int capacity=150,weight=0,value=0;
		for(int i=0;i<articles.length&&weight<capacity;i++) {
			int newWeight=weight+articles[i].weight;
			if(newWeight<=capacity) {
				weight=newWeight;
				value+=articles[i].value;
				selectedArticles.add(articles[i]);
			}
		}
		for(int i=0;i<selectedArticles.size();i++) {
			System.out.println(selectedArticles.get(i));
		}
		System.out.println(weight);
		System.out.println(value);
		
	}
	public static void main(String[] args) {
		//价值主导
		select("价值主导",(Article a1,Article a2)->{	
			return a2.value-a1.value;
		});
		//重量主导
		select("重量主导",(Article a1,Article a2)->{	
					return a1.weight-a2.weight;
				});
		//价值主导
		//a2.valueOfDensity-a1.valueOfDensity;结果为double型 而迭代器要求返回类型为int
		//Double.compare(double d1,doouble d2)返回int型
		select("价值密度主导",(Article a1,Article a2)->{	
					return Double.compare(a2.valueOfDensity, a1.valueOfDensity);
				});
		
	}

}