Checking for special type of Arrays in JavaScript

We are required to write a JavaScript function that takes in an array of literals and checks if elements are the same or not if read from front or back. Such arrays are also known by the name of palindrome arrays.

Some examples of palindrome arrays are:

const arr1 = ['a', 'b', 'c', 'b', 'a'];
const arr2 = [4, 7, 7, 4];
const arr3 = [7, 7, 7, 7, 7, 7];

Method 1: Using a For Loop

This approach compares elements from both ends moving towards the center:

const arr = [1, 5, 7, 4, 15, 4, 7, 5, 1];
const isPalindrome = arr => {
    const { length: l } = arr;
    const mid = Math.floor(l / 2);
    for(let i = 0; i 

true
false
true


Method 2: Using Array.reverse() and join()

This method converts the array to string and compares it with its reversed version:

const isPalindromeReverse = arr => {
    return arr.join(',') === arr.slice().reverse().join(',');
};

const testArray1 = [1, 2, 3, 2, 1];
const testArray2 = [1, 2, 3, 4, 5];

console.log(isPalindromeReverse(testArray1));
console.log(isPalindromeReverse(testArray2));


true
false


Method 3: Using Two Pointers

This efficient approach uses two pointers moving from opposite ends:

const isPalindromeTwoPointers = arr => {
    let left = 0;
    let right = arr.length - 1;
    
    while (left 

true
false
true


Comparison

Conclusion

The two-pointer approach offers the best combination of efficiency and readability for checking palindrome arrays. It uses constant space and only needs to iterate through half the array elements.