Leetcode: Reverse Vowels of a String

Write a function that takes a string as input and reverse only the vowels of a string.

Example 1:
Given s = "hello", return "holle".

Example 2:
Given s = "leetcode", return "leotcede".

Note:
The vowels does not include the letter "y".

 1 public class Solution {
 2     public String reverseVowels(String s) {
 3         StringBuffer res = new StringBuffer(s);
 4         int l=0, r=s.length()-1;
 5         while (l < r) {
 6             while (l<r && !isVowel(res.charAt(l))) l++;
 7             while (l<r && !isVowel(res.charAt(r))) r--;
 8             if (l == r) break;
 9             char temp = res.charAt(l);
10             res.setCharAt(l, res.charAt(r));
11             res.setCharAt(r, temp);
12             l++;
13             r--;
14         }
15         return res.toString();
16     }
17     
18     public boolean isVowel(char c) {
19         if (c==‘a‘ || c==‘e‘ || c==‘i‘ || c==‘o‘ || c==‘u‘|| c==‘A‘ || c==‘E‘ || c==‘I‘ || c==‘O‘ || c==‘U‘) return true;
20         else return false;
21     }
22 }