自定义hash键C++

struct Key {
    std::string first;
    std::string second;
};

struct KeyHash {
 std::size_t operator()(const Key& k) const
 {
     return std::hash<std::string>()(k.first) ^
            (std::hash<std::string>()(k.second) << 1);
 }
}; //位运算，移位运算

struct KeyEqual {
 bool operator()(const Key& lhs, const Key& rhs) const
 {
    return lhs.first == rhs.first && lhs.second == rhs.second;
 }
};

 // 定义 KeyHash 与 KeyEqual 结构体并在模板中使用它们
    std::unordered_map<Key, std::string, KeyHash, KeyEqual> m6 = {
            { {"John", "Doe"}, "example"},
            { {"Mary", "Sue"}, "another"}
    };
 

/*template <class Key,  ：主键的类型
 *            class T,    ：被映射的值的类型
 *            class Hash = hash<Key>, ：一元，以一个key类型对象为参数
 *            返回一个基于该对象的size_t类型的唯一值,类模板内部，使用其别名为hasher的成员类型
 *            class Pred = equal_to<Key>, 二元谓词，以两个Key类型的对象为参数，返回一个bool值
 *            如果第一个参数等价为第二个参数，该bool值为true,否则为false.默认值为std::equal_to
 *            class Alloc = allocator< pair<const Key, T> >
 *            容器内部用来管理内存分配及释放的内存分配器的类型
 * > class unordered_map; 
 *template<class Key> struct hash; 
 *
 */

#include <iostream>
#include <ctime>
#include <string>
#include <vector>
#include <fstream>
#include <unordered_map>
#include <utility>
#include <stack>
#include <sstream>
using namespace std;

/***********物体属性******/
class item
{
public:
    long value; //物体价值
    int weight; //物体重量
    item() : value(0), weight(0) {}
};
/***********包含物体数量以及背包容量的键值对象,映射的value为目前容量下所能获得的最优价值*************/
class Key
{
public:
    long weight;       //
    int number;
    Key(int _num, long _weight) :  number(_num), weight(_weight) {}
};

struct KeyHash   //自定义Hash函数
{
    size_t operator()(const Key& k) const
    {
        return std::hash<long>()(k.weight) ^
                (std::hash<int>()(k.number) << 1);
    }
};

struct KeyEqual  //自定义操作符号
{
    bool operator()(const Key& lhs, const Key& rhs) const
    {
        return lhs.number == rhs.number && lhs.weight == rhs.weight;
    }
};

class Knapsack
{
public:
/**************构造函数读取数据*************/
    Knapsack()
    {
        ifstream fin("1.txt");
        string line;
        stringstream stream;
        if(getline(fin, line))
        {
            stream.clear();
            stream << line;
            stream >> knapsack_size;
            stream >> num_of_items;
        } 
        int cnt = 1;
        init_items();

        while(getline(fin, line))
        {
            long _value;
            long _weight;
            stream.clear();
            stream << line;
            stream >> _value;
            stream >> _weight;
            items[cnt].value = _value;
            items[cnt].weight = _weight;
            cnt++;
        }
    }
    
    void init_items()
    {
        items.resize(num_of_items+1);
    }
    void dynamic() //递归动态规划
    {
        long max_value = make(num_of_items, knapsack_size);
        cout << "max_value:" << max_value << endl;
    }
    

    long make(int i_item, long weight)
    {
        Key find_key(i_item, weight);
        unordered_map<Key, long, KeyHash, KeyEqual >::iterator got = map.find(find_key);
        if( got != map.end())
        {
            return got->second;
        } 
        long value1 = 0;
        long value2 = 0;
        if(i_item == 0)  //0件物品的情况
        {

            Key temp_key(0, weight);
            map.insert(make_pair(temp_key, 0));
            return 0;
        }
        value1 = make(i_item-1, weight);
        
        if(weight >= items[i_item].weight)
        {
            
            value2 = make(i_item-1, weight-items[i_item].weight) + items[i_item].value;
            if(value2 > value1)
            {
                Key temp_key(i_item, weight);
                map.insert(make_pair(temp_key, value2));
            } else {
                Key kk(i_item, weight);
                map.insert(make_pair(kk, value1));
                cout << value1 << endl;
            }
            
        } else {
            Key temp_key(i_item, weight);
            map.insert(make_pair(temp_key, value1));
        }
        return value1 > value2 ? value1 : value2;
    }
/**************根据hash表存储的值找到最优解集合****************/
    void reconstruct()
    {
        int i = num_of_items;
        int weight = knapsack_size;
        while(i > 0)
        {
            Key k1(i, weight);
            Key k2(i-1, weight);
            unordered_map<Key, long, KeyHash, KeyEqual>::iterator got1 = map.find(k1);
            unordered_map<Key, long, KeyHash, KeyEqual>::iterator got2 = map.find(k2);
            
            if(got1 != map.end() && got2 != map.end())
            {
                if( (got1->second > got2->second) && (weight-items[i].weight >=0) )
                {
                    set.push_back(i);
                    weight -= items[i].weight;
                    i--;
                } else {
                    i--;
                }
            }
        }
    }
    
/********打印看结果*********/
    void print()
    {
        ofstream fout1;
        fout1.open("out1.txt");
        for(int i = 0; i < set.size(); i++)
        {
            fout1  << set[i] << " " ;
        }
        fcout << endl;

        
    }


public:
    vector<item> items; 
    int num_of_items;    //物品个数
    long knapsack_size;  //背包容量
    unordered_map<Key, long, KeyHash, KeyEqual> map;  //自定义哈希键值
    vector<int> set; //存储最优解
};


int main()
{
    clock_t start, end;
    start = clock();
    Knapsack knapsack;
    knapsack.dynamic();
    knapsack.reconstruct();
    knapsack.print();
    end = clock();
    cout << "running time:" << (double)(end-start)/CLOCKS_PER_SEC << "s" << endl;
    return 0;
}