freeCodeCamp/guide/english/certifications/coding-interview-prep/project-euler/problem-4-largest-palindrome-product/index.md

title
Largest palindrome product

Problem 4: Largest palindrome product

Method:

• A palindromic number is the one that when reversed reads the same.
• The largest number obtained from product of two 3 digit number is 999 * 999, so we can make a loop that starts by producting the largest number and check if that number is palindromic or not.

Solution:

function largestPalindromeProduct(n) {
  
  //To get the maximum n digit number, + operator type castes String to Number type
  let max = +[...Array(n)].reduce((a, c) => a+=9, "");
  
  //Next we get minimum n digit number from the max
  let min = (max+1)/10;
  
  //To store the result
  let res = [];
  
  //Starting the loop from max to min
  for (let i = max; i >= min; i--){
    
    //Another loop 
    for (let j =  max; j >= min; j--){
      
      //Getting the product
      let num = i*j; 
      
      //Reversing the number
      let numReverse = [...String(num)].reverse().join('');
      
      //Checking for palindromic number
      if (num == numReverse) {
      
        //Pushing the number into array and breaking the loop for efficiency
        res.push(num);
        break;
      }
    }
  }
  
  // Returning the maximum of the result array
  return Math.max(...res);
}

• Run Code

References:

• Wikipedia