palindromeChainLength.js

/**
 * Description:
 *
 * Number is a palindrome if it is equal to the number with digits in reversed order.
 * For example, 5, 44, 171, 4884 are palindromes and 43, 194, 4773 are not palindromes.
 *
 * Write a method palindrome_chain_length which takes a positive number and returns the number of special steps needed
 * to obtain a palindrome. The special step is: "reverse the digits, and add to the original number".
 * If the resulting number is not a palindrome, repeat the procedure with the sum until the resulting number is a palindrome.
 *
 * If the input number is already a palindrome, the number of steps is 0.
 *
 * Input will always be a positive integer.
 *
 * For example, start with 87:
 *
 * 87 + 78 = 165; 165 + 561 = 726; 726 + 627 = 1353; 1353 + 3531 = 4884
 *
 * 4884 is a palindrome and we needed 4 steps to obtain it, so palindrome_chain_length(87) == 4
 */
let palindromeChainLength = n => {

    let reverNum = n => Array.from(n.toString()).reverse().join('')
    let isPalindrome = n => reverNum(n) === n.toString()

    let steps = 0
    while (!isPalindrome(n)) {
        steps++
        n += parseInt(reverNum(n))
    }

    return steps
}