回复：回复：Yes, I think C(6,3)*2*2+6!/6=200..

来源: 于 2012-05-04 08:56:10 [旧帖] [给我悄悄话] 本文已被阅读：次

Two parts:

There are C(6,3)*C(3,3)=20 cases. For one case,{[a1,a2,a3],[a4,a5,a6]}={[a4,a5,a6],[a1,a2,a3]}.But we have {(a1a2a3,a4a5a6),(a1a2a3,a4a6a5),(a1a3a2,a4a5a6),(a1a3a2,a4a6a5)} 2*2=4 cases for book changes.20*4=80.

a1a2a3 : a1 to a2,a2 to a3 and a3 to a1.

One part:

6!/6=120. round permutation.

80+120=200.