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".

vowels:元音aeiou

解法：two pointers

public class Solution {
    public String reverseVowels(String s) {
        String vowel = "aeiouAEIOU";
        int start = 0;
        int end = s.length()-1;
        char[] chars = s.toCharArray();
        while(start<end)
        {
            while(start<end&&!vowel.contains(chars[start]+""))
            {
                start++;
            }
            while(start<end&&!vowel.contains(chars[end]+""))
            {
                end--;
            }
            
            char temp = chars[start];
            chars[start]=chars[end];
            chars[end]=temp;
            start++;
            end--;
        }
        
        return String.valueOf(chars);
        
    }
}

chars[end]+"" 这里加上“”很重要，不然会出以下错误：

error: incompatible types: char cannot be converted to CharSequence