leetcode[Reverse Vowels of a String]

public class Solution {
    public String reverseVowels(String s) {
        char[] c = s.toCharArray();
        int head = 0;
        int tail = c.length - 1;
        HashSet<Character> set = new HashSet<>(Arrays.asList('a', 'A', 'e', 'E',
        		'i', 'I', 'o', 'O', 'u', 'U'));
        while(head < tail){
        	//遇到数组都先考虑是否可能有数组下标越界！
        	while(head < c.length && !set.contains(c[head++]));//head不能超出c.length，都是因为在循环体内的移动
        	head--;//定位到要交换的字符
        	while(tail >= 0 && !set.contains(c[tail--]) );//tail不能小于0，都是因为在循环体内的移动
        	tail++;//定位到要交换的字符
        	//System.out.println("head: " + head + c[head] + "    " + "tail: " + tail + c[tail]);
        	//开始交换，交换之前还要判断一次head是否小于tail，因为在最外层循环体内还有移动
        	if(head < tail){
            	char t = c[head];
            	c[head] = c[tail];
            	c[tail] = t;
        	}
        	//head,tail往中间挪动
        	head++;
        	tail--;
        }
        return new String(c);
    }
}