6174 is the Kaprekar constant. All natural numbers less than 10,000 (except some with same digits) can be reduced to 6174 in the following steps:
Order the digits of the number in descending and ascending order and compute the difference. Repeat the process till you get 6174.
Example
n = 2376
Digits in descending order = 7632
Digits in ascending order = 2367
Step1:
>> 7632 - 2367 ans = 5265
Step 2:
>> 6552 - 2556 ans = 3996
Step3:
>> 9963 - 3699 ans = 6264
Step4
>> 6642 - 2466 ans = 4176
Step5
>> 7641 - 1467 ans = 6174
Total number of steps = 5.
Your function should return the number of Kaprekar steps for a given input. Numbers such as 2222 will end in zero. These numbers will never result in 6174. They should return Inf.
Solution Stats
Problem Comments
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9 Comments
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6 older comments
Muthu Annamalai
on 17 Apr 2012
The behavior at x=6174 is artifically set to 0, which taints the pure-recursive solution, but hey it was cool problem!
Jean-Marie Sainthillier
on 3 Aug 2012
The K constant is 495 for 3 digits.
So the test with 691 is wrong.
Why tests with only one digit ?
Did I miss something ?
Grzegorz Knor
on 14 Sep 2012
I don't understand the Test Suite for x = 3 and x = 1 too. what should I do in this case?
Tim
on 14 Sep 2012
For x=3, the steps are 3000-0003=2997, 9972-2799=7173, etc.
Marcel
on 25 Dec 2013
Problem description is confusing as there are different Kaprekar constants depending on the number of digits. [0 9 495 6174 for 1, 2,3 4 digits respectively.
Georges
on 30 Sep 2014
getting this error:
Internal Server Error - Read
The server encountered an internal error or misconfiguration and was unable to complete your request.
Reference #3.c2c1ab8.1412090777.18623697
any ideas?
Thorsten Bartel
on 22 May 2017
The problem should specify that any number with less than four digits should be filled up to four digits with leading zeros. (e.g. 3 -> 0003)
Jesús Zambrano
on 29 Jan 2019 at 12:31
Very nice and interesting problem!
Florian Roscheck
on 4 Feb 2019 at 6:21
I like the recursion aspect of this problem.
Solution Comments
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1 Comment
Serhii Tetora
on 22 Jan 2019 at 8:35
How it works with x = 3, x = 691, x = 1?
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2 Comments
Steffen Zelzer
on 8 Feb 2018
This works for all but test 3 where it gives, in my opinion, the correct answer 8.
TurqoiseInt
on 13 Feb 2018
But zero is not sorted in this solution. You should get same answer for input x = 691 and 6910. (And then no need for abs())
1) 9610-0169=9441
2) 9441-1449=7992
3) 9972-2799=7173
4) 7731-1377=6354
5) 6543-3456=3087
6) 8730-0378=8352
7) 8532-2358=6174
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1 Comment
Chuck Saunders
on 1 Feb 2018
This has been the lamest test so far. You need to pad the numbers with zeros to build it up to be a 4 digit number. Not explained in the rules.
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1 Comment
Kwin
on 18 Jul 2017
Not all test cases seem to be correct. For example x=3 would imply that the next value should be x=3-3=0, so y_correct=Inf and not 6
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1 Comment
Jon
on 31 Dec 2014
An efficient lookup table solution
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1 Comment
Peter Wittenberg
on 30 Mar 2012
Interesting - a recursive approach
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1 Comment
blaat
on 10 Feb 2012
Could you stop doing this kind of thing? I think it would be a lot more fun if we could see the _actual_ best solution..
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