Policy Based Data Structures C++

#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>
using namespace   std;
using namespace __gnu_cxx;
using namespace __gnu_pbds;


//ordered statistics tree...can be modified to long long, pair<int, int> , greater<int>....etc
typedef tree< int, null_type, less< int >, rb_tree_tag, tree_order_statistics_node_update > ordered_set;
template <typename T> using orderedSet = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;// C++11 is a must
//find_by_order(k) -> returns pointer to the k th order element, order_of_key(x) -> returns position of key x