什么！map中的排序算法从来没用过！

用户9831583

发布于 2022-06-16 15:09:19

2120

发布于 2022-06-16 15:09:19

文章被收录于专栏：码出名企路

map定义：

template < class Key, class T, class Compare = less<Key>, 
    class Allocator = allocator<pair<const Key,T> > > class map;

1 Key 和 Value。

2 第四个是 Allocator，用来定义存储分配模型的。 3 第三个参数：class Compare = less<Key>。

什么? map中也可以定义排序算法，还是万能模板，好吧，今后面试排序就靠它类。

 #include <iostream>                                                   
 #include <string>                               
 #include <map>                                   
    class Name
    {
        private:
            std::string firstname{}; 
            std::string secondname{};
        public:
            Name(std::string first, std::string second) : firstname{first},
                 secondname{second}{};
            Name()=default;
            bool operator>(const Name& name)const
            {
                return secondname > name.secondname ||
                    ((secondname == name.secondname) &&
                         (firstname > name.firstname));
            }
          friend std::ostream& operator<<(std::ostream& out, const Name& name);
    };

    inline std::ostream& operator<<(std::ostream& out, const Name& name)
    {
        out << name.firstname + " " + name.secondname;
        return out;
    }

   int main()
{
       std::map<Name,size_t, std::greater<Name>> people{{Name{"Al", "Bedo"}, 53}, 
                            {Name{"Woody","Leave"},33},{Name{"Noah", "Lot"}, 43}};
        for ( const auto& p : people)
            std::cout << p.first << " " << p.second << " \n";

        return 0;
   }

万能？你再来一个看看。

#include <iostream>                                              
#include <string>                               
#include <map>                                   
 #include <memory>
 using std::string;
 using namespace std;

class Key_compare
{
public:
    bool operator () (const unique_ptr<string>& p1,
                     const unique_ptr <string>& p2) const
{
        return *p1 < *p2;
    }
};

int main()
{  
    //第三个参数用来比较
   std::map<unique_ptr<string>,string,Key_compare> phonebook;
    //在容器的适当位置直接生成了一个 pair 对象
    //14
    phonebook.emplace(make_unique<string>("Fred"), "914 626 7897");
    //将参数元素移到容器中
    phonebook.insert(make_pair(make_unique<string>("Lily"), "212 896 4337"));
    for (const auto& p: phonebook)
        std:: cout << *p.first << " " << p.second << std::endl;

    for (auto iter = std::begin (phonebook) ;iter != std:: end (phonebook) ; ++iter)
        std:: cout << *iter->first << " " << iter->second << std::endl;
    
    return 0;
}