#include <iostream>
#include <tuple>
#include <unordered_map>
using namespace std;
 
using coord1D = std::size_t;
using coord2D = std::pair<coord1D,coord1D>;
struct pair_hash {
    template <class T1, class T2>
    std::size_t operator() (const std::pair<T1, T2> &pair) const {
        return std::hash<T1>()(pair.first) ^ std::hash<T2>()(pair.second);
    }
};
class matrix {
	std::unordered_map<coord2D, double, pair_hash> m; 
public: 
	auto& operator[] (pair<int,int> p) { 
		if (p.first>p.second)
		    p = make_pair(p.second, p.first);
		return m[p];
	}
};
 
int main() {
	matrix m;
	m[make_pair(1,5)] = 27.2;
	cout << m[make_pair(1,5)]<<" "<<m[make_pair(5,1)]<<endl;
	return 0;
}

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