Policy Based Data Structure

#include<bits/stdc++.h>
using namespace std;
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define ll long long
typedef tree<
pair<ll,ll>,
     null_type,
     greater<pair<ll,ll> >,
     rb_tree_tag,
     tree_order_statistics_node_update> set_t;

int main()
{
    set_t arnob;
    arnob.insert(make_pair(5,10));
    arnob.insert(make_pair(1,9));
    arnob.insert(make_pair(7,9));
    arnob.insert(make_pair(5,7));
    for(auto x : arnob){
       cout<<x.first<<' '<<x.second<<endl;
    }cout<<endl;

    pair<ll,ll> pp = *(arnob.find_by_order({2}));
    cout<<pp.first<<' '<<pp.second<<endl;

    cout<<arnob.order_of_key(pp)<<endl;
    return 0;
}