345. Reverse Vowels of a String

Problem Statement Source

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 lower and upper cases, more than once.

Example 1:

Input: s = “hello” Output: “holle”

Example 2:

Input: s = “leetcode” Output: “leotcede”

Constraints:

• 1 <= s.length <= 3 * 10^5
• s consist of printable ASCII characters.

1. Read the question first.
2. Two Pointers [Try to think in this direction]

Solution:

class Solution {
    public String reverseVowels(String s) {
        char[] charArr = s.toCharArray();
        String vowels = "aeiouAEIOU";
        int i = 0;
        int j = s.length() - 1;  // Start from the end of the string
    
        while (i < j) {
            while (i < j && !vowels.contains(String.valueOf(charArr[i]))) {
                i++;
            }
 
            while (i < j && !vowels.contains(String.valueOf(charArr[j]))) {
                j--;
            }
 
            // Swap the vowels at positions i and j
            if (i < j) {
                char temp = charArr[i];
                charArr[i] = charArr[j];
                charArr[j] = temp;
                i++;
                j--;
            }
        }
 
        return new String(charArr);
    }
}