is_smooth.cpp

bool isSmooth(std::vector<int> arr) {
    auto first = std::begin(arr);
    auto last  = std::rbegin(arr);
    
    if (*first == *last) {
        if ((arr.size() % 2) == 0) {
            std::advance(first, arr.size() / 2);
            auto next = std::prev(first);
            return (*first + *next) == *last;
        } else {
            std::advance(first, arr.size() / 2);
            return *first == *last;
        }
    } else {
        return false;
    }
}