Imagine that you are blind and have been given some coins from your friend. Every coins has two sides which have different color (black and white). With only flipping the coins, you must partitioned the coin so that there are the same number between white coin and black coin.
Please note that you cannot count the number of each sides. Assume you are given n coins with b black coins. The solution is deterministic. So.. probabilistic solution is not accepted...
Okay guys, have a nice thinking :)