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".

Solution：前后two pointers, 交换vowels

Time Complexity: O(N) Space Complexity: O(N)

Solution Code：

class Solution {
    public String reverseVowels(String s) {
        if(s == null || s.length()==0) return s;
        String vowels = "aeiouAEIOU";
        char[] chars = s.toCharArray();
        int i = 0, j = s.length() - 1;
        while(i < j){
            // skip non-vowels
            while(i < j && !vowels.contains(chars[i] + "")) i++;
            while(i < j && !vowels.contains(chars[j] + "")) j--;

            // change vowels
            char tmp = chars[i];
            chars[i] = chars[j];
            chars[j] = tmp;

            i++;
            j--;
        }
        return new String(chars);
    }
}