|The British Informatics
the computing competition for schools and colleges.
We are proud to present BIO'99.
The 1999 British Informatics
I have a pack of six cards, all clubs - A23456. I split the pack into two halves, A23 and 456, then interleave them with the 4 on top; in other words I do a single in-riffle shuffle changing the order to 4A5263. Using the same shuffle a second time gives 246A35. A third identical shuffle returns the pack to its original order.
Given a pack of n cards and a method of shuffling them, we are interested in how many times this shuffle must be repeated before the pack is restored to its original order. The in-riffle shuffle on six cards restores the original order with 3 shuffles; it requires 52 shuffles for a pack of 52 cards. The corresponding out-riffle shuffle, which interleaves placing the top card of the other pile on top, takes 4 shuffles with 6 cards and 8 shuffles with 52 cards.
Write a program that first inputs an integer n (1<=n<=100), followed by n lines each containing a single integer. These n lines describe a shuffle; if the kth of these lines is l it indicates the card in position k moves to position l after the shuffle. You should output the number of times this shuffle must be repeated for the original order to be restored.
All the input shuffles will be well-formed. In other words, the values on the n lines will be an arrangement of the numbers 1,...n without omission or repetition. No shuffle on up to 100 cards requires more than 2^28 repetitions.
6 2 4 6 1 3 5