NC222435. [USACOFeb2021P]CountingGraphs
描述
Bessie has a connected, undirected graph G with N vertices labeled 1…N and M edges %7D)
. G may contain self-loops (edges from nodes back to themselves), but no parallel edges (multiple edges connecting the same endpoints).
Let%7D)
be a boolean function that evaluates to true if there exists a path from vertex 1 to vertex a that traverses exactly b edges for each 1≤a≤N and 0≤b, and false otherwise. If an edge is traversed multiple times, it is included that many times in the count.
Elsie wants to copy Bessie. In particular, she wants to construct an undirected graph G′ such that%3Df_G(a%2Cb)%7D)
for all a and b.
Your job is to count the number of distinct graphs G′ that Elsie may create, modulo
. As with G, G′ may contain self-loops but no parallel edges (meaning that there are 
distinct graphs on N labeled vertices in total).
Each input contains%7D)
test cases that should be solved independently. It is guaranteed that the sum of 
over all test cases does not exceed 105.
Let
Elsie wants to copy Bessie. In particular, she wants to construct an undirected graph G′ such that
Your job is to count the number of distinct graphs G′ that Elsie may create, modulo
Each input contains
输入描述
The first line of the input contains T, the number of test cases.
The first line of each test case contains the integers N and M.
The next M lines of each test case each contain two integers x and y (1≤x≤y≤N), denoting that there exists an edge between x and y in G.
Consecutive test cases are separated by newlines for readability.
输出描述
For each test case, the number of distinct G′ modulo 109+7 on a new line.
示例1
输入:
1 5 4 1 2 2 3 1 4 3 5
输出:
3
说明:
In the first test case, G′ could equal G or one of the two following graphs:
5 4 1 2 1 4 3 4 3 5
5 5 1 2 2 3 1 4 3 4 3 5
示例2
输入:
7 4 6 1 2 2 3 3 4 1 3 2 4 1 4 5 5 1 2 2 3 3 4 4 5 1 5 5 7 1 2 1 3 1 5 2 4 3 3 3 4 4 5 6 6 1 2 2 3 3 4 4 5 5 6 6 6 6 7 1 2 2 3 1 3 1 4 4 5 5 6 1 6 10 10 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 1 10 22 28 1 2 2 3 3 4 4 5 5 6 6 7 1 7 1 8 3 9 8 10 10 11 10 12 10 13 10 14 11 15 12 16 13 17 14 18 9 15 9 16 9 17 9 18 15 19 19 20 15 20 16 21 21 22 16 22
输出:
45 35 11 1 15 371842544 256838540
说明:
These are some larger test cases. Make sure to output the answer modulo 109+7. Note that the answer for the second-to-last test case is 245(mod109+7).