# 0345. Reverse Vowels of a String

<https://leetcode.com/problems/reverse-vowels-of-a-string>

## Description

Given a string `s`, reverse only all the vowels in the string and return it.

The vowels are `'a'`, `'e'`, `'i'`, `'o'`, and `'u'`, and they can appear in both cases.

**Example 1:**

```
**Input:** s = "hello"
**Output:** "holle"
```

**Example 2:**

```
**Input:** s = "leetcode"
**Output:** "leotcede"
```

**Constraints:**

* `1 <= s.length <= 3 * 105`
* `s` consist of **printable ASCII** characters.

## ac

```java
class Solution {
    public String reverseVowels(String s) {
        // edge cases
        if (s.length() <= 1) return s;

        char[] chars = s.toCharArray();
        int l = 0, r = chars.length - 1;
        while (l < r) {
            while (l < r && !isVowel(chars[l])) l++;
            while (l < r && !isVowel(chars[r])) r--;
            char tmp = chars[l];
            chars[l++] = chars[r];
            chars[r--] = tmp;
        }

        return String.valueOf(chars);
    }

    private boolean isVowel(char c) {
        c = Character.toLowerCase(c);
        if (c == 'e' || c == 'u' || c == 'o' || c == 'i' || c == 'a')
            return true;
        return false;
    }
}
```