freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-javascript/6a1d9f98e819ed70a0e994da.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
6a1d9f98e819ed70a0e994da	Challenge 328: Kaprekar's Routine	28	challenge-328

--description--

Given a 4-digit number, return the number of times you need to apply Kaprekar's routine until reaching 6174.

Kaprekar's routine works as follows:

• Arrange the digits in descending order to form the largest number
• Arrange the digits in ascending order to form the smallest number (pad with leading zeros if necessary)
• Subtract the smaller from the larger
• Repeat with the new number

--hints--

kaprekar(1234) should return 3.

assert.equal(kaprekar(1234), 3);

kaprekar(2025) should return 6.

assert.equal(kaprekar(2025), 6);

kaprekar(7173) should return 4.

assert.equal(kaprekar(7173), 4);

kaprekar(3164) should return 7.

assert.equal(kaprekar(3164), 7);

kaprekar(8082) should return 2.

assert.equal(kaprekar(8082), 2);

--seed--

--seed-contents--

function kaprekar(n) {

  return n;
}

--solutions--

function kaprekar(n) {
  let steps = 0;
  let current = n;

  while (current !== 6174) {
    const digits = String(current).padStart(4, "0").split("").map(Number);
    const desc = parseInt(digits.slice().sort((a, b) => b - a).join(""));
    const asc = parseInt(digits.slice().sort((a, b) => a - b).join(""));
    current = desc - asc;
    steps++;
  }

  return steps;
}