is_lucky.cpp

bool isLucky(int n) {
    auto sum = [](auto c) {
        return std::accumulate(std::begin(c), std::end(c), 0);
    };
    
    auto str   = std::to_string(n);
    auto left  = str.substr(0, str.size() / 2);
    auto right = str.substr(str.size() / 2);
    
    return sum(left) == sum(right);
}