自定义set比较函数

#include <iostream>
#include <set>
#include <string>
using namespace std;
struct node
{
    int a,b;
    node(int aa, int bb)
    {a=(aa),b=(bb);}

};
struct cmp
{
    bool operator()(node s1,node s2)
    {
        if( s1.a != s2.a )
        return s1.a > s2.a;
        return s1.b>s2.b;
    }
};
set<node, cmp>words;
int main()
{
 words.insert(node(1,1));
 words.insert(node(2,1));
 words.insert(node(3,2));
 words.insert(node(4,3));
 words.insert(node(5,3));
 words.insert(node(5,-2));
 set<node>::iterator mbegin;
 set<node>::iterator mend = words.end();
 for( mbegin = words.begin(); mbegin != mend; ++mbegin)
  cout<<mbegin->a<<" "<<mbegin->b<<endl;
 return 0;
}