Hi, guys ... This is my first blog ... I am completely new to algorithms ... I have just taken it up and I really love it ... I love searching for puzzles each day and try solving them... right now, i am very bad at it ... I hope to improve ASAP and be good one day ... cheers... A problem for u all so that u dont get bored ;) 

You are given a set S of n numbers. You must pick a subset S' of k numbers from S such that the probability of each element of S occurring in S' is equal (i.e., each is selected with probability k/n). You may make only one pass over the numbers. What if n is unknown?