JavaScriptReverseVowelsOfAString.md

JavaScript Reverse Vowels of a String

Challenge

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.

1^st Example

Input: s = 'hello'
Output: 'holle'

2^nd Example

Input: s = 'leetcode'
Output: 'leotcede'

Constraints

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

Solution

const reverseVowels = (s) => {
    let vowels = ['a', 'A',
                  'e', 'E',
                  'i', 'I',
                  'o', 'O',
                  'u', 'U'],
        stack  = [];

    for (let i = 0; i < s.length; i++) {
        if (vowels.indexOf(s[i]) !== -1) {
            stack.push(s[i]);
        }
    }

    let ans = [];

    for (let i = 0; i < s.length; i++) {
        if (vowels.indexOf(s[i]) !== -1) {
            ans.push(stack.pop());
        } else {
            ans.push(s[i]);
        }
    }

    return ans.join('');
};

Explanation

I've coded a function called reverseVowels that takes a string s as input. The purpose of this function is to reverse the vowels in the input string and return the modified string.

The function begins by creating an array called vowels that contains all the vowels in both uppercase and lowercase.

Next, an empty array called stack is created. This array will be used to store the vowels encountered in the input string.

A for loop is used to iterate through each character of the input string s . Within the loop, an if statement checks if the current character is a vowel by using the indexOf method to search for the character in the vowels array. If the character is a vowel, it is pushed into the stack array.

After that, an empty array called ans is created. This array will store the modified string with reversed vowels.

Another for loop is used to iterate through each character of the input string s . Within this loop, an if statement checks if the current character is a vowel by using the indexOf method to search for the character in the vowels array. If the character is a vowel, it is replaced with the last vowel in the stack array by using the pop() method. This effectively reverses the order of the vowels.

If the current character is not a vowel, it is simply pushed into the ans array.

Finally, the ans array is converted to a string using the join() method with an empty string as the separator. The resulting modified string is then returned as the output of the function.

In summary, this function iterates through the input string twice. The first iteration collects the vowels in the stack array, and the second iteration replaces the vowels in the input string with the vowels from the stack array in reverse order. The modified string is then returned as the output of the function.

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