#include <algorithm>
#include <string>

template <typename T>
class ReverseComparator{
    public:
     bool operator()(T l, T r){return !(l < r);}
};

int main() {
    std::string str = "HELLO";
    ReverseComparator<char> comparator;
    std::sort(str.begin(), str.end(), comparator);
}