I can not solve it,please tell me how to solve it,thank you!^_^

You can do this for all edges:
1 - delete edge
2 - find shortest way (Deikstra) between 2 vertex, which
are connetcted with this edge
3 - insert edge
 This solution (O(N^4))pass time limits

P.S.
It may done in N^3 with Deikstra for each vertex
I don't know how to do this :(

Is there anything to do with Hamiltonian circuit ?

Hamiltonian circuit for n=100 ?!?!?!
We will die before your program will give us an answer :O

Well... it's not always true that Hamiltonian related problems are NP completed.

You can always use some heuristics that will reduce it to polynomial time...

so don't be so marked ^^

Floyd n^3

http://tadvent.wordpress.com/2009/02/14/%E6%9C%80%E5%B0%8F%E7%8E%AF-%E4%B8%8E-floyd/

Thank you for the hint.