JavaScript Program to Reverse Consonants in a Given String Without Affecting the Other Elements

In this article, we have given a string and the task is to write a javascript program to reverse only the consonants of a string without affecting the other elements’ positions and printing the output in the console.

Examples:

Input: hello
Output: lelho
Explanation: h,l,l are consonants in the given string. 
After modifying the string their occurrences are l,l,h and 
vowels positions are not changed.

These are the following approaches by using these we can solve the given question:

Using loop:

In this approach, we reverse the consonants in a given string. It initializes pointers at the start and end of the string, identifies consonants using a set, and swaps them until the pointers meet. If a character is not a consonant, the corresponding pointer is incremented or decremented accordingly. The code converts the array of characters back to a string and returns the modified string.

Example: This example shows the use of the above-explained approach.

Javascript

// Function to reverse the
// consonants of the given string
function reverseConsonants(s) {
    // Convert string to array of characters
    let sArray = s.split('');

    // Initialize pointers
    let left = 0;
    let right = s.length - 1;

    // Define set of consonants
    let consonants = new Set(['b', 'c', 'd', 'f', 'g',
        'h', 'j', 'k', 'l', 'm', 'n', 'p', 'q', 'r', 's',
        't', 'v', 'w', 'x', 'y', 'z']);

    // While pointers don't meet
    while (left < right) {
        if (consonants.has(sArray[left].toLowerCase())
            && consonants.has(sArray[right].toLowerCase())) {
            // Swap consonants
            let temp = sArray[left];
            sArray[left] = sArray[right];
            sArray[right] = temp;
            left++;
            right--;
        } else if (!consonants.has(sArray[left].toLowerCase())) {
            left++;
        } else if (!consonants.has(sArray[right].toLowerCase())) {
            right--;
        }
    }

    // Convert array back to string and return
    return sArray.join('');
}

// Driver Code
let s = 'geek';
console.log(reverseConsonants(s));

Output

keeg

Using reverse() method:

In this approach, the function generates a consonant list from the input string using array operations. It reverses this list, initializes an empty string, and iterates through the input, replacing consonants with reversed ones. It utilizes the ‘match()‘ method for character checks, array methods like ‘filter()‘ and ‘reverse()‘, and string concatenation to build the modified string, which is then returned.

Example: This example shows the use of the above-explained approach.

Javascript

function reverseConsonants(inputString) {

    // Generate a list of consonants
    // from the input string
    let consonants = Array.from(inputString).
        filter(char =>
            char.match(/[a-zA-Z]/) && !'aeiouAEIOU'.includes(char));

    // Reverse the list of consonants
    consonants.reverse();

    // Initialize a string variable
    // to store the modified string
    let outputString = '';

    // Iterate through the input string and replace
    // consonants with reversed consonants
    for (let char of inputString) {
        if (char.match(/[a-zA-Z]/) && !'aeiouAEIOU'.includes(char)) {
            outputString += consonants.shift();
        } else {
            outputString += char;
        }
    }

    // Return the modified string
    return outputString;
}

let inputString = "geek";
console.log(reverseConsonants(inputString));

Output

keeg