Answer by NutCracker for How to find if a given key exists in a std::map

I know this question already has some good answers but I think my solution is worth of sharing.

It works for both std::map and std::vector<std::pair<T, U>> and is available from C++11.

template <typename ForwardIterator, typename Key>bool contains_key(ForwardIterator first, ForwardIterator last, Key const key) {    using ValueType = typename std::iterator_traits<ForwardIterator>::value_type;    auto search_result = std::find_if(        first, last,        [&key](ValueType const& item) {            return item.first == key;        }    );    if (search_result == last) {        return false;    } else {        return true;    }}