class Solution {
public:
    bool IsLetter(char ch)
    {
        if((ch >='a'&& ch <='z')
            ||(ch >='A'&&ch <='Z'))
            return true;
        else
            return false;
    }
    string reverseOnlyLetters(string s) {
        if(s =="")
            return s;
        size_t begin = 0,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;
    }
};