Project Euler: #4 - Largest palindrome product

Problem

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.

Problem Description

A palindromic number reads the same both forward and also backward.

One such palindromic number is 9009 which is the largest palindrome made by multiplying two 2-digit numbers, 91 * 99

We need to find the largest Palindrome that can be made by multiplying two 3-digit numbers

Approach

The smallest 3-digit number is 100 and the largest is 999. Since we need the largest palindrome, we approach this from the largest to the smallest, 999 -> 100.

Two reversed for loops starting from 999 for each number, eg: 99 * 99, 99 * 98, 99 * 97 etc

To check if the product is Palindrome,

convert the number to string,
then split it into an array,
reverse the array &
join the items to get the reversed number in string format.
Now convert the reversed number to a number format and compare with the original number.
If both are equal, then it is a palindrome.

Solution

const checkPalindrome = (number) => {
    let reverse = String(number)
        .split('')
        .reverse()
        .join('');
      return Number(reverse) === number;
}

const retLargestPalindrome = () => {
    let maxVal = 0;

    for (let i = 999; i >= 100; i--) {
        for (let j = 999; j >= 100; j--) {
            let prod = i * j;
            if (checkPalindrome(prod)) {
                if (prod > maxVal) maxVal = prod;
                // Can also use maxVal = Math.max(maxVal, prod);
                break;
            }
        }
    }
    return maxVal;
}

console.log(retLargestPalindrome());

My Solution is found in 04

If you have another or a better solution, please leave it in the comments below.

For the other Project Euler Solutions, please follow the series Project Euler Solutions in JS.

Thank you!

Project Euler: #4 - Largest palindrome product

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