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

public class Solution {
    public String reverseVowels(String s) {
        if(s == null) return null;
        int left = 0;
        int right = s.length() - 1;
        char[] tmp = s.toCharArray();
        while(left < right) {
            while( !isVowel(tmp[left]) && left < right) left++;
            while( !isVowel(tmp[right]) && left < right) right--;
            if(left >= right) break;
            // swap and continue;
            char t = tmp[left];
            tmp[left] = tmp[right];
            tmp[right] = t;

            left++;
            right--;
        }
        return new String(tmp);
    }

    public boolean isVowel(char a) {
        return a == 'a' || a == 'e' || a == 'i' || a == 'o' || a == 'u' ||
                a == 'A' || a == 'E' || a == 'I' || a == 'O' || a == 'U';
    }
}