Problem

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”

Note: The vowels does not include the letter “y”.

Pre analysis

Will keep two pointers. iterate both of them until reaching a vowel and swap their places.

Another Solution

Syntactical sugar + clean approach

var reverseVowels = function(s) {

    const swap = (arr, i, j) => {
    let tmp = arr[i];
    arr[i] = arr[j];
    arr[j] = tmp;
    };

    //----------------------------//
    const vowels = ['a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U']; // include upper case here, no need to check toLowerCase() for each char

    let strArr = s.split('');
    let l = 0, r = strArr.length - 1;

    while (l < r) {
    if (!vowels.includes(strArr[l])) {
        l++;
    } else if (!vowels.includes(strArr[r])) {
        r--;
    } else {
        swap(strArr, l, r);
        l++;
        r--;
    }
}
return strArr.join('');