TheDrizzyWay / Kaprekar-s-Constant

Kaprekar's Constant

Context

Take any four-digit number (whose digits are not all identical) and do the following;

1. Rearrange the string of digits to form the largest and smallest 4-digit numbers possible.
2. Take these two numbers and subtract the smaller number from the larger.
3. Use the number you obtain and repeat the above process.

The most amazing thing is this: ​Every ​ four digit number whose digits are not all the same will eventually hit 6174, in at most 7 steps, and then stay there!

Task

Write an algorithm to compute the Kaprekar’s constant on any four-digit number. The algorithm must do the following:

1. Take ​only ​four-digit numbers whose digits are not identical.
2. Return the number of steps taken to get to the Kaprekar’s constant (6174).
   Example: using 3524.

5432 – 2345 = 3087

8730 – 0378 = 8352

8532 – 2358 = ​6174

7641 – 1467 = ​6174

This above example should return “3”, because it took 3 steps to get to the constant.

UI Design

1. An input text field to collect the four-digit number.
2. Buttons to perform the operation.
3. Div to display result.

A live demo of this challenge can be found on Codepen