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".

一刷
题解：
与344类似，不过这回只有元音字母需要交换位置，方法相同，two pointer

public class Solution {
    public String reverseVowels(String s) {
        char[] vowals = "aeiouAEIOU".toCharArray();
        char[] ss = s.toCharArray();
        Set<Character> dict = new HashSet<Character>();
        for(char a : vowals){
            dict.add(a);
        }
        int l = 0, r = s.length()-1;
        while(l<r){
            while(!dict.contains(ss[l]) && l<r) l++;
            while(!dict.contains(ss[r]) && l<r) r--;
            if(l<r){
                char temp = ss[l];
                ss[l] = ss[r];
                ss[r] = temp;
                l++;
                r--;
            }
        }
        return new String(ss);
    }
}

二刷
思路同上