class Solution {
public:
    bool isLetter(char ch)
    {
        if(ch >= 'a' && ch <= 'z')
        {
            return true;
        }
        if(ch >= 'A' && ch <= 'Z')
        {
            return true;
        }
        return false;
    }
    string reverseOnlyLetters(string s) {
        if(s.empty())
        {
            return s;
        }
        size_t begin = 0;
        size_t end = s.size()-1;
        while(begin < end)
        {
            while(begin < end && !isLetter(s[begin]))
            {
                ++begin;
            }
            while(begin < end && !isLetter(s[end]))
            {
                --end;
            }
            swap(s[begin],s[end]);
            ++begin;
            --end;
        }
        return s;
    }
};