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

(1) Java

class Solution {
    public String reverseVowels(String s) {
        Set<Character> vowels = new HashSet<>(Arrays.asList('a','o','u','e','i', 'A','O','U','E','I'));
        int i = 0; 
        int j = s.length()-1;
        StringBuilder sb = new StringBuilder(s);
        while (i < j) {
            while (i < j && !vowels.contains(s.charAt(i))) {
                i++;
            }
            while (j > i && !vowels.contains(s.charAt(j))) {
                j--;
            }
            if (i < j) {
                char c1= s.charAt(i);
                char c2= s.charAt(j);
                sb.setCharAt(i, c2);
                sb.setCharAt(j, c1);
                i++;
                j--;
            }
        }
        return sb.toString();
    }
}

(2) Python

(3) Scala