力扣917仅仅反转字母

利用下标去访问，在判断是不是字符，最后交换后再去前后加加就可以了 

class Solution {
public:

	bool source(char monitor)
	{
		if (monitor >= 'a' && monitor <= 'z')
			return true;
		if (monitor >= 'A' && monitor <= 'Z')
			return true;
		return false;
	}
	string reverseOnlyLetters(string s) {
		size_t skim, scroll;
		skim = 0;
		scroll = s.size() - 1;
		while (skim < scroll)
		{
			while (skim < scroll && !source(s[skim]))
				skim++;
			while (skim < scroll && !source(s[scroll]))
				scroll--;

			swap(s[skim], s[scroll]);
			skim++;
			scroll--;
		}

		return s;
	}
};