Leetcode 345. Reverse Vowels of a String

public class Solution {    public String reverseVowels(String s) {        HashSet<Character> hs = new HashSet<>();        hs.add('a');        hs.add('e');        hs.add('i');        hs.add('o');        hs.add('u');        hs.add('A');        hs.add('E');        hs.add('I');        hs.add('O');        hs.add('U');                int low = 0, high = s.length()-1;        StringBuilder sb = new StringBuilder(s);        while (low < high) {            while (low < high && !hs.contains(sb.charAt(low))) low++;            while (low < high && !hs.contains(sb.charAt(high))) high--;            // swap low and high            char tmp = sb.charAt(low);             sb.setCharAt(low, sb.charAt(high));             sb.setCharAt(high, tmp);            low++;            high--;        }                return sb.toString();    }}