Amur Leopard

Knuth Shuffle

chtangwin — Wed, 25 Mar 2009 02:56:00 +0000

How to shuffle a deck of cards in a fast efficient way? Or, given an array of length n (e.g. 10000) and natural numbers from 1 to n, how to reorder the data series to be as random as possible (random permutation)? This is a classic computer science question, and it makes a good technical interview question.

Knuth shuffle algorithm is an elegant and fast algorithm to do shuffling. Let X1, X2…. XN be the set of N numbers to be shuffled.

   1. Set j to N
   2. Generate a random number R. (uniformly distributed between 0 and 1)
   3. Set k to (jR+1). k is now a random integer, between 1 and j.
   4. Exchange Xk and Xj
   5. Decrease j by 1.
   6. If j > 1, return to step 2.

void KnuthShuffle(int* pArr)
{
	int rand;
	for(int i=N-1; i>=0; i--)
	{
		rand = GenRand(0,i);
		swap (pArr[i], pArr[rand]);
	}
}

Note: The algorithm is copied from here which has more detailed information.

Brian Beckman: I have an idea, then what?

chtangwin — Mon, 21 Jan 2008 01:13:42 +0000

Another Brian Beckman video, on the topic of invention, patent, etc.

http://channel8.msdn.com/Posts/Brian-Beckman-I-have-an-idea-then-what/

Brian Beckman: Don’t fear the Monads

chtangwin — Sun, 20 Jan 2008 09:30:38 +0000

One of the favorite exercises on the web nowadays is to write Monads tutorial. I struggled through the concept until having seen this video from Brian Beckman of Microsoft Research.:

http://channel9.msdn.com/Showpost.aspx?postid=358968

It is a terrific video and explain Monad in the context of function “composability”. Highly recommended!!

I will write a short summary of my understanding when I get time.

Welcome

chtangwin — Tue, 08 Jan 2008 19:23:14 +0000

Welcome to my first weblog.

The Amur Leopard (Panthera pardus orientalis or Panthera pardus amurensis) is the rarest subspecies of leopard and the rarest cat on Earth, according to Answer.com.