Reverse Vowels of a String

1-reverse-vowels.js

/* Approach 1. Loop through string and store vowels on array, placeholders in string. Then loop through string again and replace in vowels in reverse order. */
var reverseVowels = function(s) {
    var result = '';
    
    var string = [];
    var vowels = [];
    
    // Start from front of string to find consonants and vowels.
    for (var i=0; i<s.length; i++) {
        var orig = s[i];
        var char = s[i].toLowerCase();

        if (char === 'a' || char === 'e' || char === 'i' || char === 'o' || char === 'u') {
            vowels.push(orig);
            orig = null; // placeholder
        }

        string.push(orig);
    }

    // Insert vowels.
    for (var i=0; i<string.length; i++) {
        if (!string[i]) {
            string[i] = vowels.splice(vowels.length - 1, 1)[0];
        }
    }
    
    result = string.join('');
    
    return result;
}

2-reverse-vowels.js

/* Approach 2. Loop through string and convert to array, storing vowels in 2nd array. Then loop through vowels and swap in two at a time in reverse order. Finally, join array back into string. */
/**
 * @param {string} s
 * @return {string}
 */
var reverseVowels = function(s) {
    var result = '';
    
    var string = [];
    var vowels = { A: 1, a: 1, E: 1, e: 1, I: 1, i: 1, O: 1, o: 1, U: 1, u: 1 };
    var vowelsToReverse = [];
    
    for (var i=0; i<s.length; i++) {
        if (vowels[s[i]]) {
            // Store the character and its position (to swap with end of list).
            vowelsToReverse.push({ char: s[i], pos: i });
        }
        
        // Regardless, just append.
        string.push(s[i]);
    }
    
    // Insert vowels into position.
    while (vowelsToReverse.length) {
        var vowel1 = vowelsToReverse.splice(0, 1)[0];
        var vowel2 = null;
        
        if (vowelsToReverse.length) {
            vowel2 = vowelsToReverse.splice(vowelsToReverse.length - 1, 1)[0];
        }
        
        if (vowel2) {
            string[vowel1.pos] = vowel2.char;
            string[vowel2.pos] = vowel1.char
        }
    }
    
    result = string.join('');
    
    return result;
};

3-reverse-string.js

/* Approach 3. Fastest! Convert the string to an array. Maintain a pointer at the front and end of string.
   End will point to the first vowel found from the end.
   If the current letter is a consonant, do nothing and advance to next letter.
   If the current letter is a vowel, swap it with the end pointer, and decrement end to the next vowel.
   When the front passes the end, we're done.
*/
var reverseVowels = function(s) {
    var result = '';
    var str = s.split('')
    
    var end = s.length - 1;
    for (var i=0; i<str.length; i++) {
        if (i > end) {
            // We're done.
            break;
        }

        // Find first vowel from end of string.
        while (end >= 0) {
            if ('aAeEiIoOuU'.indexOf(str[end]) !== -1) {
                // We have a vowel.
                break;
            }
            
            end--;
        }
        
        if ('aAeEiIoOuU'.indexOf(str[i]) === -1) {
            // Consonant, do nothing.
        }
        else {
            // Vowel, swap with end.
            var temp = str[end];
            str[end] = str[i];
            str[i] = temp;
            
            end--;
        }
    }
    
    result = str.join('');
    
    return result;
}

zexample.txt

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".