algorithm - Order Statistic Tree in C++

Question

I need an order statistic tree for standard GCC STL map containers.

I checked and there is something known as PBDS. Policy based data structures. That usage is also not clear to me.

Anyone can tell me how to use STL map containers for order statistic tree? Even if its only on GNU G++ its enough?

Answer 1

Here is the example of GNU Policy-Based STL MAP implemented as order statistic tree (tested on Linux gcc 4.6.1):

#include <iostream>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

typedef
tree<
  int,
  int,
  less<int>,
  rb_tree_tag,
  tree_order_statistics_node_update>
map_t;

int main()
{
  map_t s;
  s.insert(make_pair(12, 1012));
  s.insert(make_pair(505, 1505));
  s.insert(make_pair(30, 1030));
  cout << s.find_by_order(1)->second << '
';
  return 0;
}

Here is a link to the overview of GNU Policy-Based Data Structures. Here is other tree_order_statistics example. I cannot find a good reference for Policy-Based Data Structures, but you can use these links as well as PBDS sources.