#include <iostream>

#include <string>

#include <utility>

#include <unordered_map>

// print out a std::pair

template <class Os, class U, class V>

Os& operator<<(Os& os, const std::pair<U,V>& p) {

return os << '{' << p.first << ", " << p.second << '}';

}

// print out an associative container

template <class Os, class K, class V>

Os& operator<<(Os& os, const std::unordered_map<K, V>& v) {

os << '[' << v.size() << "] { ";

bool o{};

for (const auto& e : v)

os << (o ? ", " : (o = 1, "")) << e;

return os << " }\n";

}

int main()

{

std::unordered_map<std::string, int>

p{ {"C", 3}, {"B", 2}, {"A", 1}, {"A", 0} },

q{ {"E", 6}, {"E", 7}, {"D", 5}, {"A", 4} };

std::cout << "p: " << p << "q: " << q;

p.merge(q);

std::cout << "p.merge(q);\n" << "p: " << p << "q: " << q;

}