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Tree orientation.

Revision en3, by Loud_Scream, 2017-09-04 23:56:44

Hi, Codeforces. I've recently found an interesting problem:

Given an undirected tree with n vertices. Find out how many different ways you can orient the edges of the tree so that the result graph will contain exactly m vertices with zero outdegree modulo 109 + 7,   (1 ≤ n ≤ 1000, 0 ≤ m ≤ n).

Could someone help me with this problem and explain the solution?

#### History

Revisions

Rev. Lang. By When Δ Comment
en3 Loud_Scream 2017-09-04 23:56:44 5 Tiny change: 'outdegree by module $10^9 + 7' -> 'outdegree modulo$10^9 + 7'
en2 Loud_Scream 2017-09-04 23:55:22 0 (published)
en1 Loud_Scream 2017-09-04 23:54:58 403 Initial revision (saved to drafts)