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”.

不多说了，类似题目：https://blog.jing.do/4766

public class Solution {
    public String reverseVowels(String s) {
        if(s == null || s.length()==0) return s;
        String vowels = "aeiouAEIOU";
        char[] chars = s.toCharArray();
        int start = 0;
        int end = s.length()-1;
        while(start<end){

            while(start<end && !vowels.contains(chars[start]+"")){
                start++;
            }

            while(start<end && !vowels.contains(chars[end]+"")){
                end--;
            }

            char temp = chars[start];
            chars[start] = chars[end];
            chars[end] = temp;

            start++;
            end--;
        }
        return new String(chars);
    }
}