set is very useful in OI. Several common functions qwq are summarized.

#include<iostream>
#include<cstdio>
#include<set>
//set Common usage of containers 
using namespace std;
                                                    //Customized sorting rules can be achieved by using parody functions 
class R
{
    public:
    bool operator()(const int &pre,const int &bac)
    {
        return pre>bac;//Guarantee that the sequence is larger before than after 
    }
};
set<int/*,R*/> s;                                    //If you remove the comment, you will use a parody function. 
int main()
{
    s.insert(5);
    s.insert(4);
    s.insert(3);
    s.insert(2);
    s.insert(1);
    
    for(set<int>::iterator i=s.begin();i!=s.end();i++)
        cout<<*i<<" ";                                //print 1 2 3 4 5 
        
    //erase
    cout<<endl<<"Erase";                                
    cout<<endl<<s.erase(3)<<endl;                    //Delete successfully returns 1, otherwise return 0 
    
    for(set<int>::iterator i=s.begin();i!=s.end();i++)
        cout<<*i<<" ";                                //print 1 2 4 5
    
    //uper_bound & lower_bound
    //uper_bound(x):Return s Medium satisfaction is greater than x Iterator of Minimum Element 
    //lower_bound(x):Return s Medium satisfies greater than or equal to x Iterator of Minimum Element 
    cout<<endl<<"uper_bound & lower_bound";
    cout<<endl<<*s.upper_bound(3);                    //print 4
    
    cout<<endl<<*s.lower_bound(3)<<endl;            //print 4
    
    cout<<endl<<*s.upper_bound(4);                    //print 5
    
    cout<<endl<<*s.lower_bound(4)<<endl;            //print 4
    
    cout<<endl<<(s.lower_bound(6)==s.end())<<endl;    //print 1  When none of the elements is greater than or equal to 6, the tail iterator is returned 
    
    //insert
    cout<<endl<<"insert"<<endl;
    s.insert(6); 
    
    for(set<int>::iterator i=s.begin();i!=s.end();i++)
        cout<<*i<<" ";                                //print 1 2 4 5 6
    return 0;
}

It's worth noting that when we change the rules with parody functions to make the sequence from big to small, the meaning of upper_bound and lower_bound is not what the annotations describe. Now the functions of these two functions will be very strange. Let me illustrate the functions of these two functions with a simple non-professional description for any situation.

lower_bound(x) :

1. When there is an element equal to x in the container, return the element iterator
2. Otherwise, assuming that x is inserted into the appropriate location of the container according to the arrangement rules of the container elements, the iterator of the next (right) element of X after the insertion is returned, and the tail iterator is returned if there are no elements.

exa.

• 653 221 x = 4, assuming that after insertion: 654 321, the iterator returns element 3
• %^ &* (, suppose inserting (suppose this is an ordered sequence),%^ &* (return iterator of element% at this time)

upper_bound(x) :

There are no rules for lower_bound(x). Same as others