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:
Input: "hello"
Output: "holle"
Example 2:
Input: "leetcode"
Output: "leotcede"

// correct 

May use a HashSet to reduce the look up time to O(1)

public class Solution {
public String reverseVowels(String s) {
    if(s == null || s.length()==0) return s;
    String vowels = "aeiouAEIOU";
    char[] chars = s.toCharArray();
    int start = 0;
    int end = s.length()-1;
    while(start<end){
        
        while(start<end && !vowels.contains(chars[start]+"")){
            start++;
        }
        
        while(start<end && !vowels.contains(chars[end]+"")){
            end--;
        }
        
        char temp = chars[start];
        chars[start] = chars[end];
        chars[end] = temp;
        
        start++;
        end--;
    }
    return new String(chars);
}






// compile error 




class Solution {
    public String reverseVowels(String s) {
      HashSet<Character> set = new HashSet<>(){'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'};
      
      char[] word = s.toCharArray();
      int i = 0;
      int j = s.length() - 1;
      while( i < j){
        while( i < j && !set.contains(word[i])){
          i++;
        }
        while( i < j && !set.contains(word[j])){
          j--;
        }
        char tmp = word[i];
        word[i] = word[j];
        word[j] = tmp;
        i++;
        j--;
      }
      return new String(word);
      
        
    }
}