Order Set

#include<bits/stdc++.h>

#include<ext/pb_ds/assoc_container.hpp>

#include<ext/pb_ds/tree_policy.hpp>

#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>

#define endl "\n\n"

using namespace __gnu_pbds;

using namespace std;

int main()

{

    ordered_set os;

    os.insert(10);

    os.insert(13);

    os.insert(7);

    os.insert(9);

    os.insert(8);

    os.insert(3);

    os.insert(5);

    os.insert(1);

    cout << "Order Set is :: ";

    for(auto i : os)

        cout << i << " ";

    cout << endl;

    cout << "3rd index value : " << *(os.find_by_order(3)) << endl;

    cout << "Number of value less than 8 :: " << os.order_of_key(8) << endl;

    cout << "Number of value less than 5 :: " << os.order_of_key(5) << endl;

    /// Delete value 7 if it exist in Order Set

    if(os.find(7) != os.end())

        os.erase(os.find(7));

    cout << "After Deleting 7 The Order Set is :: ";

    for(auto i : os)

        cout << i << " ";

    cout << endl;

    cout << "After Deleting 3rd index is :: " << *(os.find_by_order(3)) << endl;

    cout << "After Deleting Number of Value less than 8 :: " << os.order_of_key(8) << "\n";

    return 0;

}

For more details : Link