Reverse Only Letters

Given a string S, return the "reversed" string where all characters that are not a letter stay in the same place, and all letters reverse their positions.

 


Example 1:

Input: "ab-cd"
Output: "dc-ba"

Example 2:

Input: "a-bC-dEf-ghIj"
Output: "j-Ih-gfE-dCba"

Example 3:

Input: "Test1ng-Leet=code-Q!"
Output: "Qedo1ct-eeLg=ntse-T!"

 

Note:

  1. S.length <= 100
  2. 33 <= S[i].ASCIIcode <= 122 
  3. S doesn't contain \ or "

Solution:

class Solution {
    public String reverseOnlyLetters(String S) {
        char[] arr = S.toCharArray();
        int left = 0, right = S.length() - 1;
        while (left < right) {
            char a = arr[left];
            char b = arr[right];
            if (!Character.isLetter(a)) {
                left ++;
            } else if (!Character.isLetter(b)) {
                right --;
            } else {
                char temp = arr[left];
                arr[left ++] = arr[right];
                arr[right --] = temp;
            }
        }
        return new String(arr);
    }
}