20bits - Latest Comments in Interview Questions: Shuffling an Array

Re: Interview Questions: Shuffling an Array

gman — Fri, 20 Nov 2009 11:52:04 -0000

I was asked this question in an interview. I gave the seemingly correct but subtly wrong solution. Good to know the correct solution.

Re: Interview Questions: Shuffling an Array

Hanna — Tue, 26 Aug 2008 15:08:39 -0000

Hi,
Great effort after reading this I really good very nice point how to shuffle array keep it up
and post more article also check Pre Developer

Thanks

Re: Interview Questions: Shuffling an Array

Andy — Sat, 12 Apr 2008 10:14:10 -0000

What if the source and destination are picked using a random number generator N times? Given that the generator is unifrom, aren't all permutations possible?

Re: Interview Questions: Shuffling an Array

phil — Fri, 11 Apr 2008 04:35:19 -0000

rue, see here: http://eigenclass.org/hiki....

Re: Interview Questions: Shuffling an Array

Jesse — Thu, 10 Apr 2008 21:39:02 -0000

rue,

That's not really true, though. In fact, that "solution" violates multiple requirements of the problems.

One, it's not in-place. Two, whether or not the distribution is uniform depends on the sorting algorithm that <tt>sort_by</tt> uses.

Re: Interview Questions: Shuffling an Array

rue — Thu, 10 Apr 2008 17:06:49 -0000

Excellent note about the algorithm.

However, since pragmatism trumps all, the "right" way to shuffle an Array in Ruby is this:

class Array
def shuffle!
replace(array.sort_by { rand })
end
end

As a bonus, it is a language/core lib bug and not your fault if there is a problem with the distribution ;)

Re: Interview Questions: Shuffling an Array

Jesse — Thu, 10 Apr 2008 13:00:27 -0000

cc,

You're right about the first point, but not the second. Both self.size and size work because we're inside the Array instance.

Re: Interview Questions: Shuffling an Array

cc — Thu, 10 Apr 2008 06:15:53 -0000

Note: - I could be wrong here but I think you're code example#1 has a typo, you define variable r and don't use it, and use variable k and don't define it

and shouldn't it be n= self.size in example#1 as well as example#2?

Re: Interview Questions: Shuffling an Array

phil — Thu, 10 Apr 2008 05:38:08 -0000

For yet another Ruby implementation of Array#shuffle see Random numbers in Ruby, http://snippets.dzone.com/p...

Nice post!

Re: Interview Questions: Shuffling an Array

Chris — Wed, 09 Apr 2008 14:50:34 -0000

I enjoy reading the posts on this blog. The posts related to programming are entertaining and help exercise my brain.

>> My next article is going to be more about the interview process rather than specific questions

Regarding the interview process, I've found this post very helpful.
http://www.joelonsoftware.c...
Joel Spolsky has also written a book ("Smart and Gets Things Done") which elaborates on the same ideas in the blog post.