题意：求一个图中点数为S的完全子图个数
思路：直接搜，一个强剪枝就是只连单向边，可以减少一半规模的搜索
#include<bits/stdc++.h>
using namespace std;
const int maxn = 105;
vector<int>e[maxn];
int mp[maxn][maxn];
int n,m,s,ans;
void dfs(int u,int *tmp,int siz)
{
if(siz==s)
{
ans++;
return;
}
for(int i = 0;i<e[u].size();i++)
{
int v = e[u][i];
int flag = 0;
for(int j=1;j<=siz;j++)
if(!mp[v][tmp[j]] || !mp[tmp[j]][v])
{
flag=1;
break;
}
if(!flag)
{
siz++;
tmp[siz]=v;
dfs(v,tmp,siz);
tmp[siz]=0;
siz--;
}
}
}
int main()
{
int T;
scanf("%d",&T);
while(T--)
{
ans = 0;
scanf("%d%d%d",&n,&m,&s);
for(int i = 0;i<=n;i++)e[i].clear();
memset(mp,0,sizeof(mp));
for(int i = 1;i<=m;i++)
{
int u,v;
scanf("%d%d",&u,&v);
e[u].push_back(v);
mp[u][v]=mp[v][u]=1;
}
int siz;
for(int i = 1;i<=n;i++)
{
siz = 1;
int tmp[12];
tmp[1]=i;
dfs(i,tmp,1);
}
printf("%d\n",ans);
}
}
Problem Description
A clique is a complete graph, in which there is an edge between every pair of the vertices. Given a graph with N vertices and M edges, your task is to count the number of cliques with a specific size S in the graph.
Input
The first line is the number of test cases. For each test case, the first line contains 3 integers N,M and S (N ≤ 100,M ≤ 1000,2 ≤ S ≤ 10), each of the following M lines contains 2 integers u and v (1 ≤ u < v ≤ N), which means there is an edge between vertices u and v. It is guaranteed that the maximum degree of the vertices is no larger than 20.
Output
For each test case, output the number of cliques with size S in the graph.
Sample Input
3
4 3 2
1 2
2 3
3 4
5 9 3
1 3
1 4
1 5
2 3
2 4
2 5
3 4
3 5
4 5
6 15 4
1 2
1 3
1 4
1 5
1 6
2 3
2 4
2 5
2 6
3 4
3 5
3 6
4 5
4 6
5 6
Sample Output
3 7 15
Source
2016ACM/ICPC亚洲区沈阳站-重现赛（感谢东北大学）
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