# LeetCode - 0917. Reverse Only Letters
### 題目網址：https://leetcode.com/problems/reverse-only-letters/
###### tags: `LeetCode` `Easy` `字串`

/*
    -LeetCode format-
    Problem: 917. Reverse Only Letters
    Difficulty: Easy
    
    by Inversionpeter
*/



class Solution {
public:
    string reverseOnlyLetters(string S) {
        int first = 0, second = S.size() - 1;
        while (1) {
            while (first != S.size() && !isalpha(S[first]))
                ++first;
            while (second >= 0 && !isalpha(S[second]))
                --second;
            if (first >= second)
                break;
            swap(S[first], S[second]);
            ++first; --second;
        }
        return S;
    }
};