c++ - 如何为多集和地图使用基于策略的数据结构？

Question

以下代码适用于ordered_set（其中不允许重复）（CREDITS：GFG）：

// C++ program to demonstrate the 
// ordered set in GNU C++

#include <iostream>

using namespace std; 

// Header files, namespaces, 
// macros as defined above 
#include <ext/pb_ds/assoc_container.hpp> 
#include <ext/pb_ds/tree_policy.hpp> 
using namespace __gnu_pbds; 

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

// Driver program to test above functions 
int main() 
{ 
    // Ordered set declared with name o_set 
    ordered_set o_set; 

    // insert function to insert in 
    // ordered set same as SET STL 
    o_set.insert(5); 
    o_set.insert(1); 
    o_set.insert(2); 

    // Finding the second smallest element 
    // in the set using * because 
    //  find_by_order returns an iterator 
    cout << *(o_set.find_by_order(1))<< endl;
return 0; 
}

如何对允许重复值的多重集（也适用于映射、对、多重映射）使用相同的值。

我想使用类似的东西：

#define ordered_pair tree < pair<int, int> , null_type ,  less ,  rb_tree_tag , tree_order_statistics_node_update >

或者

#define ordered_map tree < map<int, int> , null_type ,  less ,  rb_tree_tag ,  tree_order_statistics_node_update >;

但它会引发错误：

error: type/value mismatch at argument 3 in template parameter list for ‘template<class Key, class Mapped, class Cmp_Fn, class Tag, template<class Node_CItr, class Node_Itr, class Cmp_Fn_, class _Alloc_> class Node_Update, class _Alloc> class __gnu_pbds::tree’
typedef tree < pair<int, int> ,  null_type ,  less ,  rb_tree_tag ,  tree_order_statistics_node_update > ordered_set;

标签： c++stl