200623: [AtCoder]ARC062 F - Painting Graphs with AtCoDeer

Memory Limit:512 MB Time Limit:2 S
Judge Style:Text Compare Creator:
Submit:0 Solved:0

Description

Score : $1300$ points

Problem Statement

One day, AtCoDeer the deer found a simple graph (that is, a graph without self-loops and multiple edges) with $N$ vertices and $M$ edges, and brought it home. The vertices are numbered $1$ through $N$ and mutually distinguishable, and the edges are represented by $(a_i,b_i) (1≦i≦M)$.

He is painting each edge in the graph in one of the $K$ colors of his paint cans. As he has enough supply of paint, the same color can be used to paint more than one edge.

The graph is made of a special material, and has a strange property. He can choose a simple cycle (that is, a cycle with no repeated vertex), and perform a circular shift of the colors along the chosen cycle. More formally, let $e_1$, $e_2$, $...$, $e_a$ be the edges along a cycle in order, then he can perform the following simultaneously: paint $e_2$ in the current color of $e_1$, paint $e_3$ in the current color of $e_2$, $...$, paint $e_a$ in the current color of $e_{a-1}$, and paint $e_1$ in the current color of $e_{a}$.

Figure $1$: An example of a circular shift

Two ways to paint the edges, $A$ and $B$, are considered the same if $A$ can be transformed into $B$ by performing a finite number of circular shifts. Find the number of ways to paint the edges. Since this number can be extremely large, print the answer modulo $10^9+7$.

Constraints

  • $1≦N≦50$
  • $1≦M≦100$
  • $1≦K≦100$
  • $1≦a_i,b_i≦N (1≦i≦M)$
  • The graph has neither self-loops nor multiple edges.

Input

The input is given from Standard Input in the following format:

$N$ $M$ $K$
$a_1$ $b_1$
$a_2$ $b_2$
$:$
$a_M$ $b_M$

Output

Print the number of ways to paint the edges, modulo $10^9+7$.


Sample Input 1

4 4 2
1 2
2 3
3 1
3 4

Sample Output 1

8

Sample Input 2

5 2 3
1 2
4 5

Sample Output 2

9

Sample Input 3

11 12 48
3 1
8 2
4 9
5 4
1 6
2 9
8 3
10 8
4 10
8 6
11 7
1 8

Sample Output 3

569519295

Input

题意翻译

给定一张$N$个点$M$条边的无向图,每条边要染一个编号在$1$到$K$的颜色。 你可以对一张染色了的图进行若干次操作,每次操作形如,在图中选择一个简单环(即不经过相同点的环),并且将其颜色逆(顺)时针旋转一个单位。 两种染色方案被认为是本质相同的,当且仅当其中一种染色后的图经过若干次操作后可以变成另一种染色后的图。 问有多少本质不同的染色方案,输出对$10^9+7$取模。

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