I can only find 5 routes when there are 2 cities on each island : 1 2 1 3 2 3
         1 2 3 1 2 3
         1 2 3 1 3 2
         1 2 3 2 1 3
         1 3 2 1 2 3
Who can tell me the other 11 routes?

Edited by author 13.04.2004 06:02

Edited by author 13.04.2004 06:02

there are 3N -> 6 cities (2 on each island) not just 3...
eight solutions are
1 3 5 4 6 2
1 3 6 4 5 2
1 4 5 3 6 2
1 4 6 3 5 2
1 5 3 6 4 2
1 5 4 6 3 2
1 6 3 5 4 2
1 6 4 5 3 2
the other 8 are simetrical

hope I was useful.

thank you very much! Now I understand the problem.And I found the 16 routes:(2k and 2k-1 are on the same island,k=1,2,3)
1 3 5 2 4 6
1 3 5 2 6 4
1 3 6 2 4 5
1 3 6 2 5 4
1 4 5 2 3 6
1 4 5 3 2 6
1 4 6 2 3 5
1 4 6 3 2 5
1 5 2 4 6 3
1 5 3 2 4 6
1 5 3 6 2 4
1 5 4 6 2 3
1 6 2 4 5 3
1 6 3 2 4 5
1 6 3 5 2 4
1 6 4 5 2 3
And I think your routes are not correct:the tourist must go back but he can't travel from 2 to 1.Thank you all the same!