方法：双指针

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) {int len=s.size();int left=0,right=len-1;string s1;while(left<len){if(isletter(s[left])){while(!isletter(s[right]))--right;s1+=s[right];++left;--right;}else{s1+=s[left];++left;}}return s1;}
};

---

 

2. 

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 left=0,right=s.size()-1;while(left<right){while(left<right&&!isletter(s[left]))++left;while(left<right&&!isletter(s[right]))--right;swap(s[left],s[right]);++left;--right;}return s;}
};