flip_unordered_map.cpp

#include <iostream>
#include <unordered_map>  
#include <string>

template <typename T1, typename T2>
std::unordered_map<T2, T1> flip(std::unordered_map<T1, T2>& m) {
    std::unordered_map<T2, T1> result;

    for (auto&& [key, value] : m) {
        result.emplace(value, key);
    }

    return result;
};

int main() {
    std::unordered_map<std::string, int> m{{"111", 5}};    

    std::cout << m.at("111") << "\n"; // 5

    auto res = flip<std::string, int>(m);

    std::cout << res.at(5) << "\n"; // 111

    return 0;
}