345. Reverse Vowels of a String

题目：

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".

链接:

https://leetcode.com/problems/reverse-vowels-of-a-string/?tab=Description

3/12/2017

注意的问题：

1. 大小写都要包括

2. 第10， 11行需要是while不是if，而且要check start/end的合法性

public class Solution {
    public String reverseVowels(String s) {
        if (s.length() < 2) return s;

        StringBuilder sb = new StringBuilder(s);
        int start = 0, end = sb.length() - 1;
        HashSet<Character> h = new HashSet<Character>(Arrays.asList('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'));

        while (start < end) {
            while (!h.contains(sb.charAt(start)) && start < end) start++;
            while (!h.contains(sb.charAt(end)) && start < end) end--;
            if (start < end) {
                char tmp = sb.charAt(start);
                sb.setCharAt(start, sb.charAt(end));
                sb.setCharAt(end, tmp);
                start++;
                end--;
            }
        }
        return sb.toString();
    }
}