longest_strings.cpp

std::vector<std::string> allLongestStrings(std::vector<std::string> inputArray) {
    auto begin = std::begin(inputArray);
    auto end   = std::end(inputArray);
    
    auto longest_length = std::max_element(begin, end, [](auto a, auto b) {
        return a.size() < b.size();
    })->size();
    
    inputArray.erase(std::remove_if(begin, end, [&](auto s) {
        return s.size() != longest_length;
    }), end);
    
    return inputArray;
}