p****3
发帖数: 448 | 1 6 members of a book club will exchange books.
each member will give his book to another member and get a book from a
different member.
no swapping occurs (2 member get each other's book).
how many ways to arrange the exchange?
(show thoughts, not just a number) | r*****n
发帖数: 86 | 2 一点想法， 两种可能出现的loop， 一种是(a)2个3人一组的loop, 另一个是(b)6人形
成的loop. 对于a, 总共有C(6,3)种分法，而三个人之间有两种交换方法 （3-1）！,所
以总共有 C(6,3)*2*(3-1)!, 对b, 同理，C(6,6)*1*(6-1)!。 | l****h
发帖数: 272 | |
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