# CF11D A Simple Task

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• 233提交
• 题目来源
• 评测方式 RemoteJudge
• 标签 动态规划,动规,dp 枚举,暴力 状态压缩,状压
• 难度 省选/NOI-
• 时空限制 2000ms / 256MB
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求简单无向图的环数

## 题目描述

Given a simple graph, output the number of simple cycles in it. A simple cycle is a cycle with no repeated vertices or edges.

## 输入输出格式

输入格式：

The first line of input contains two integers $n$ and $m$ ( $1<=n<=19$ , $0<=m$ ) – respectively the number of vertices and edges of the graph. Each of the subsequent $m$ lines contains two integers $a$ and $b$ , ( $1<=a,b<=n$ , $a≠b$ ) indicating that vertices $a$ and $b$ are connected by an undirected edge. There is no more than one edge connecting any pair of vertices.

输出格式：

Output the number of cycles in the given graph.

## 输入输出样例

输入样例#1： 复制
4 6
1 2
1 3
1 4
2 3
2 4
3 4

输出样例#1： 复制
7


## 说明

The example graph is a clique and contains four cycles of length 3 and three cycles of length 4.

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