QOJ.ac

QOJ

Time Limit: 4 s Memory Limit: 512 MB Total points: 100 Difficulty: [show]

#2068. Fast as Ryser

統計

在阅读了论文《Counting Perfect Matchings as Fast as Ryser》之后,你学会了如何以 $O(2^n n^2)$ 的时间复杂度计算一般图中的完美匹配数量。因此,你决定编写这道题目,以鼓励大家阅读这篇论文并学习新技术。

给定一个包含 $n$ 个顶点和 $m$ 条边的无向图,以及一个常数 $c$。我们定义边集 $S$ 的权重如下:

  • 如果集合 $S$ 中有两条边共享公共顶点,则权重为 0。
  • 否则,权重为 $c^{|S|}$。注意,空集的权重为 1。

计算所有边子集的权重之和。答案可能很大,请输出其对 $10^9 + 7$ 取模的结果。

输入格式

第一行包含三个整数 $n, m, c$ ($1 \le n \le 36, 0 \le m \le \frac{n(n-1)}{2}, 1 \le c \le 10^9 + 6$)。

接下来的 $m$ 行,每行包含两个整数 $u, v$ ($1 \le u, v \le n, u \neq v$),表示图中的一条无向边 $(u, v)$。所有边均不相同。

输出格式

输出一个整数:答案。

样例

输入 1

6 10 100
3 6
1 3
2 4
3 4
4 6
1 2
4 5
2 3
1 4
3 5

输出 1

2171001

输入 2

8 11 818466928
6 7
3 6
6 5
7 3
6 2
8 1
1 7
4 3
5 1
6 1
6 4

输出 2

425176360

Discussions

About Discussions

The discussion section is only for posting: General Discussions (problem-solving strategies, alternative approaches), and Off-topic conversations.

This is NOT for reporting issues! If you want to report bugs or errors, please use the Issues section below.

Open Discussions 0
No discussions in this category.

Issues

About Issues

If you find any issues with the problem (statement, scoring, time/memory limits, test cases, etc.), you may submit an issue here. A problem moderator will review your issue.

Guidelines:

  1. This is not a place to publish discussions, editorials, or requests to debug your code. Issues are only visible to you and problem moderators.
  2. Do not submit duplicated issues.
  3. Issues must be filed in English or Chinese only.
Active Issues 0
No issues in this category.
Closed/Resolved Issues 0
No issues in this category.