• All the characters that are not English letters remain in the same position.
• All the English letters (lowercase or uppercase) should be reversed.

class Solution {
public:
    string reverseOnlyLetters(string s) {
        //用棧或者雙指標即可
        //two-pointer 
        int n=s.size();
        int left=0,right=n-1
 
;
        while(left<right)
        {
            //這樣寫是錯誤的：~((s[left]>='A'&&s[left]<='Z')||(s[left]>='a'&&s[left]<='z') 按位取反以及邏輯取非不一樣
            //寫法和快排思路相似
            while(left<right && !((s[left]>='A'&&s[left]<='Z')||(s[left]>='a'&&s[left]<='
 
z')))
            {
                //cout<<~((s[left]>='A'&&s[left]<='Z')||(s[left]>='a'&&s[left]<='z'))<<endl;
                left++;
            }
             cout<<left<<endl;
            while(left<right && !((s[right]>='A'&&s[right]<='
 
Z')||(s[right]>='a'&&s[right]<='z')))
            {
                right--;
            }
            //cout<<left<<"-"<<right<<endl;
            if(left<right)
            {
                //cout<<left<<"-"<<right<<endl;
                char tmp=s[left];
                s[left]=s[right];
                s[right]=tmp;
                left++;
                right--;
            }
        }
        return s;
    }
};