Map and set use pari as the key value. How to define

For types that do not have a default hash function , Like custom class type ,pair Type, etc , We have to do it ourselves
Specify a hash function . That's why you build directly pair Type of unordered_set Such as unordered_set<pair<int, int>> uset There will be problems

Of course , Self - defined classes ：

  You can define the structure ( class ） The operator is overloaded when , Of course, when the overloaded operator is a member function , Member functions
    Of （ Show ） The number of parameters is one less than the number of operands ,this Bind to left operand ;
    When it is not a member function , To define as a friend function , That is, add the keyword before the function friend , At this point, the parameters of the friend function
    And the number of general functions is the same

#include <iostream>
#include <algorithm>
#include <set>
#include <unordered_map>
using namespace std;

struct comp
{
    int operator()(const std::pair<int, int>& p) const {
        return p.first ^ p.second;  // The return value is bool, The comparison is &,| Are slower than this one ,
    }
};

/**
     This sum priority_queue  There is a difference ,priority_queue The higher the default value, the higher the priority , By default, sort by less than ,
     But you become bigger than , That is to change the less than row to the greater than sort , The lower the value, the higher the priority .
     But this is not priority_queue, It's right set or map Sort , Just like sort Of cmp The function has the same function ,
     The latter are sorted from small to large by default , You just changed the sort order , Sort from big to small ,
     Priority queue , Priority queue , Nature is different from ordinary containers .
     And here comp perhaps temp Is just a calling object , Compare two elements in a set , It must take two parameters , How can you and class member functions 
     Think of it together , Yes , At first, I became a member function of a class, and I put thies I wrote it out , explain C++ Learning is really not good , Of course ,
     I only saw C++ primer, There is no system to learn .
*/
struct temp
{
    bool operator()(const std::pair<int, int>& p1,const std::pair<int,int> &p2){
        if(p1.first!=p2.first)
            return p1.first > p2.first;  // The return value is bool, The comparison is &,| Are slower than this one ,
        else
            return p1.second > p2.second;
    }
};
/**
     For types that do not have a default hash function , Like custom  class  type ,pair  Type, etc , We have to do it ourselves 
     Specify a hash function . That's why you build directly  pair  Type of  unordered_set
     Such as  unordered_set<pair<int, int>> uset  There will be problems 
*/

unordered_map<pair<int,int> ,int,comp> ump; // It has been proved in practice that the coordinates are transformed into long long  A little faster than this 

int main()
{
    set<pair<int,int>, temp>st;
    for(int i=1;i<=10;++i)
        st.insert({3*i%15,i+4});    //set Only one value can be inserted at a time 
    for(auto a:st)
        cout << a.first << ' ' << a.second << endl;
    return 0;
}