345. Reverse Vowels of a String

Q:

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".

A:

就是两个指针互相交换

public class Solution {
    public String reverseVowels(String s) {
        StringBuffer buf = new StringBuffer(s);
        int i =0, j = buf.length()-1;
        Set<Character> set = new HashSet<>();
        set.add('a');
        set.add('e');
        set.add('i');
        set.add('o');
        set.add('u');
        set.add('A');
        set.add('E');
        set.add('I');
        set.add('O');
        set.add('U');
        while(i<j){
            while(i<j && set.contains(buf.charAt(i))==false)
                i++;
            while(i<j && set.contains(buf.charAt(j))==false)
                j--;
            if(i<j){
                char ch = buf.charAt(i);
                buf.setCharAt(i,buf.charAt(j));
                buf.setCharAt(j,ch);
                i++;
                j--;
            }
        }
        return buf.toString();
    }
} 

Errors:

忘了考虑大写字母的情况