codeforces#P641G. Little Artem and Graph
Little Artem and Graph
Description
Little Artem is given a graph, constructed as follows: start with some k-clique, then add new vertices one by one, connecting them to k already existing vertices that form a k-clique.
Artem wants to count the number of spanning trees in this graph modulo 109 + 7.
First line of the input contains two integers n and k (1 ≤ n ≤ 10 000, 1 ≤ k ≤ min(n, 5)) — the total size of the graph and the size of the initial clique, respectively.
Next n - k lines describe k + 1-th, k + 2-th, ..., i-th, ..., n-th vertices by listing k distinct vertex indices 1 ≤ aij < i it is connected to. It is guaranteed that those vertices form a k-clique.
Output a single integer — the number of spanning trees in the given graph modulo 109 + 7.
Input
First line of the input contains two integers n and k (1 ≤ n ≤ 10 000, 1 ≤ k ≤ min(n, 5)) — the total size of the graph and the size of the initial clique, respectively.
Next n - k lines describe k + 1-th, k + 2-th, ..., i-th, ..., n-th vertices by listing k distinct vertex indices 1 ≤ aij < i it is connected to. It is guaranteed that those vertices form a k-clique.
Output
Output a single integer — the number of spanning trees in the given graph modulo 109 + 7.
Samples
3 2
1 2
3
4 3
1 2 3
16