policy based data structure.cpp

    #include<bits/stdc++.h>
    #include <ext/pb_ds/assoc_container.hpp>
    using namespace __gnu_pbds;
    using namespace std;
    typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> indexed_set;
    int main(){
       //ios_base::sync_with_stdio(false);
       //cin.tie(NULL);
       indexed_set s;
        s.insert(2);
        s.insert(3);
        s.insert(7);
        s.insert(9);
        cout<<s.order_of_key(7);

        return 0;
    }