reverse_paren.cpp

std::string reverseParentheses(std::string s) {
    auto range_start = s.find_last_of('(');
    auto range_end   = s.find(')', range_start);

    if (range_start == std::string::npos || range_end == std::string::npos) {
        return s;
    }
    
    auto begin = std::begin(s);
    auto end   = std::begin(s);

    std::advance(begin, range_start + 1);
    std::advance(end, range_end);
    
    std::reverse(begin, end);
    
    s.erase(range_start, 1);
    s.erase(range_end - 1, 1); 

    return reverseParentheses(s);
}