力扣第917题 仅仅反转字母

class Solution {
public:
    bool isLetter(const char& c)
    {
        return 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z';
    }
    string reverseOnlyLetters(string S)
    {
        int left = 0, right = S.size() - 1;
        char temp;
        while (left < right)
        {
            while (right > left && !isLetter(S[left])) left++;
            while (right > left && !isLetter(S[right])) right--;
            if (left >= right)
            {
                break;
            }
            temp = S[left];
            S[left] = S[right];
            S[right] = temp;
            left++;
            right--;
        }
        return S;
    }
};