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……

 1     public String reverseVowels(String s) {
 2         char[] list = s.toCharArray();
 3         Set<Character> set = new HashSet<>();
 4         set.add('a');
 5         set.add('e');
 6         set.add('i');
 7         set.add('o');
 8         set.add('u');
 9         set.add('A');
10         set.add('E');
11         set.add('I');
12         set.add('O');
13         set.add('U');
14         
15         for (int i=0,j=list.length-1;i<j;)
16         {
17             if (!set.contains(list[i]))
18             {
19                 i++;continue;
20             }
21             if (!set.contains(list[j]))
22             {
23                 j--;continue;
24             }
25             
26             char temp = list[i];
27             list[i]=list[j];
28             list[j] = temp;
29             i++;
30             j--;
31         }
32         return new String(list);        
33     }