345. 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".

题目含义:反转一个字符串中的元音字母。第一个和最后一个元音字母交换，第二个和倒数第二个交换……

    public String reverseVowels(String s) {
        char[] list = s.toCharArray();
        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');
        
        for (int i=0,j=list.length-1;i<j;)
        {
            if (!set.contains(list[i]))
            {
                i++;continue;
            }
            if (!set.contains(list[j]))
            {
                j--;continue;
            }
            
            char temp = list[i];
            list[i]=list[j];
            list[j] = temp;
            i++;
            j--;
        }
        return new String(list);        
    }