REACTO - Palindrome Chain Length Problem

REACTO - Palindrome Chain Length Problem.md

REACTO - Palindrome Chain Length Problem

(From Codewars: 5kyu problem.)

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

Iterative Solution:

function palindrome_chain_length(num) {
  if (isPally(num)) {
    return 0;
  }
  let count = 0;
  while (!isPally(num)) {
    count++;
    num += reverse(num);
    count = count + PCL(num);
  }
  return count;
}

function isPally(num) {
  return String(num) === String(num).split('').reverse().join('');
}

function reverse(num) {
  return Number(num.toString().split('').reverse().join(''));
}

PCL(87); // 4884

Recursive Solution:

function palindrome_chain_length(num, count = 0) {
  if (isPally(num)) {
    return count;
  } else {
    count++;
    return PCL((num + reverse(num)), count);
  }
}

function isPally(num) {
  return String(num) === String(num).split('').reverse().join('');
}

function reverse(num) {
  return Number(num.toString().split('').reverse().join(''));
}

PCL(87); // 4884