java8新特性暴力实现背包问题例子

问题：有一个容量固定的背包和一些重量和价值都已知的物品，求背包能装下价值最高的物品组合，每个物品只能装一次

定义物品实体

/**
 * Description: 物品实体
 */
public class MyGoods {
    //名称
    private String name;
    //重量
    private int weight;
    //价值
    private int price;

    public MyGoods(String name, int weight, int price) {
        this.name = name;
        this.weight = weight;
        this.price = price;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getWeight() {
        return weight;
    }

    public void setWeight(int weight) {
        this.weight = weight;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "MyGoods{" +
                "name='" + name + '\'' +
                ", weight=" + weight +
                ", price=" + price +
                '}';
    }
}

定义背包实体

import java.util.ArrayList;
import java.util.List;

/**
 * Description: 背包
 */
public class MyPack {
    //装进来的物品名称
    private List<String> goodNames;
    //已装容量
    private int weight;
    //剩余容量
    private int hasWeight;
    //装进来的物品价值
    private int price;

    public MyPack(int hasWeight) {
        this.weight = 0;
        this.hasWeight = hasWeight;
        this.price = 0;
        goodNames = new ArrayList<>();
    }

    public boolean addGoods(MyGoods goods) {
        if (canEntry(goods)) {
            this.hasWeight -= goods.getWeight();
            this.price += goods.getPrice();
            this.weight += goods.getWeight();
            goodNames.add(goods.getName());
            return true;
        }
        return false;

    }

    public boolean canEntry(MyGoods goods) {
        return this.hasWeight >= goods.getWeight();
    }

    public List<String> getGoodNames() {
        return goodNames;
    }

    public void setGoodNames(List<String> goodNames) {
        this.goodNames = goodNames;
    }

    public int getWeight() {
        return weight;
    }

    public void setWeight(int weight) {
        this.weight = weight;
    }

    public int getHasWeight() {
        return hasWeight;
    }

    public void setHasWeight(int hasWeight) {
        this.hasWeight = hasWeight;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "MyPack{" +
                "goodNames=" + goodNames +
                ", weight=" + weight +
                ", hasWeight=" + hasWeight +
                ", price=" + price +
                '}';
    }
}

背包最大价值的组合

public static MyPack maxPrice(MyPack pack, List<MyGoods> goods) {
    //物品按重量从小到大排序
    goods.sort(Comparator.comparing(MyGoods::getWeight));
    //所有可装下的物品组合
    List<MyPack> tmps = new ArrayList<>();
    for (int i = 0; i < goods.size(); i++) {
        MyPack temPack = new MyPack(pack.getHasWeight());
        if (temPack.addGoods(goods.get(i))) {
            if(i == goods.size()-1){
                tmps.add(temPack);
                break;
            }
            int t = 0;
            for (int j = i + 1; j < goods.size(); j++) {
                if (!temPack.addGoods(goods.get(j))) {
                    tmps.add(temPack);
                    if(t==0){
                        temPack = new MyPack(pack.getHasWeight());
                        if(goods.get(i).getWeight() + goods.get(j).getWeight() <= temPack.getHasWeight()){
                            temPack.addGoods(goods.get(i));
                            j--;
                            t=1;
                        }
                    }
                }else {
                    t=0;
                    if(j==goods.size()-1){
                        tmps.add(temPack);
                    }
                }
            }

        }else {
            break;
        }
    }
    if (tmps.size() > 0) {
        //按照价值从大到小排序
        tmps.sort(Comparator.comparing(MyPack::getPrice).reversed());
        //利用java8流操作取出价值最大的
        return tmps.stream().max(Comparator.comparingInt(MyPack::getPrice)).get();
    }
    return pack;
}

测试的例子

 public static void main(String[] args) {
        //定义背包容量是10
        MyPack myPack = new MyPack(10);
        //定义物品集合
        List<MyGoods> goods = new ArrayList<>();
        goods.add(new MyGoods("b", 3, 3));
        goods.add(new MyGoods("d", 6, 5));
        goods.add(new MyGoods("a", 2, 1));
        goods.add(new MyGoods("c", 2, 2));
        goods.add(new MyGoods("e", 7, 3));
        //价值最高的组合
        MyPack maxPricePack = maxPrice(myPack, goods);
        //打印结果
        System.out.println(maxPricePack.toString());
    }

例子打印结果

MyPack{goodNames=[b, d], weight=9, hasWeight=1, price=8}