14. Reverse Only Letters.cpp

/*
Reverse Only Letters
=====================

Given a string s, reverse the string according to the following rules:

All the characters that are not English letters remain in the same position.
All the English letters (lowercase or uppercase) should be reversed.
Return s after reversing it.

Example 1:
Input: s = "ab-cd"
Output: "dc-ba"

Example 2:
Input: s = "a-bC-dEf-ghIj"
Output: "j-Ih-gfE-dCba"

Example 3:
Input: s = "Test1ng-Leet=code-Q!"
Output: "Qedo1ct-eeLg=ntse-T!"
 
Constraints:
1 <= s.length <= 100
s consists of characters with ASCII values in the range [33, 122].
s does not contain '\"' or '\\'.

Hint #1  
This problem is exactly like reversing a normal string except that there are certain characters that we have to simply skip. That should be easy enough to do if you know how to reverse a string using the two-pointer approach.
*/

class Solution {
public:
    string reverseOnlyLetters(string s) {
        int i = 0, j = s.size()-1;
        while(i < j) {
            while(i < j && !((s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z'))) i++;
            while(i < j && !((s[j] >= 'a' && s[j] <= 'z') || (s[j] >= 'A' && s[j] <= 'Z'))) j--;
            
            if(i >= j) break;
            swap(s[i], s[j]);
            i++; j--;
        }
        
        return s;
    }
};