October 30, 2009.
After a night's journey, finally we arrived at Wuhan University in the morning to participate the International Collegiate Programming Contest (ACM-ICPC).
......
Before went to sleep, my team mate Zhang and I played a popular card-game called "Builds up Train" to have a release. Although the game is a liite stupid, but it may have a lot of fun ...
Assume there are 3 kinds of cards, and each of them has unlimited supply. If we take n cards out and arrange them in a row, we can get 3n differet rows. Now the problem is, how many different rows we can get using n cards and the number of cards of each kind is even?