回复：2*4!可以理解，5!仍不太明白。anyway, thank you!
jinjing
2010-04-17 05:43:11
( reads)
We get a circle first and put 123456 on it.6 has to been connected 1 and/or 5 .If 5 between 1 and 5 OK,if out,as there four sections,two are OK two not OK.So,...