struct node
{
int id, val;
bool operator<(const node &x) const
{
if (x.id == id&&x.val==val)
return 0;
if (x.val == val)
return id < x.id;
return val < x.val;
}
};
s.insert(node{10, 200});
s.insert(node{20, 200});
s.insert(node{30, 200});
s.insert(node{
 
20, 200});
s.insert(node{10, 100});

for (set<node>::iterator it = s.begin(); it != s.end(); it++)
{
cout << (*it).id << " " << (*it).val << endl;
}

struct node
{
    int id, val;
    bool operator<(const node &x) const
    {
        if (x.id == id && x.val == val)
            
 
return 0;
        if (x.val == val)
            return id > x.id;
        return val > x.val;
    }
};
int n, m, k, a, b;
arr c;
set<node> s;
bool comp(const node &x,const node &y){
    return x.val > y.val;
}
int main()
{
    // file("test");
    // sdf(n),sdf(m),sdf(k);
    
 
// For(i, 1, n) sdf(c[i]);
    // sdf(a);
    // For(i,1,a)
    s.insert(node{10, 200});
    s.insert(node{20, 400});
    s.insert(node{30, 300});
    s.insert(node{20, 200});
    s.insert(node{10, 100});
    // s.clear();
    cout << s.size() << endl;
    set<node>::iterator it;
    it = upper_bound(s.begin(),s.end(),node{50, 200},comp);//從大到小排序的話，找第一個小於200的node
    if(it!=s.end())
        s.erase(it);
    cout<< s.count(node{20, 400}) << endl;

    for (it = s.begin(); it != s.end(); it++)
    {
        cout << (*it).id << " " << (*it).val << endl;
    }
}

set的用法