蓝桥杯 网络寻路

题目理解： 找出图中连接的三条边，起点和终点可以相同，求有多少种，直接暴力来写

#include <iostream> 
#include <cstdio>
#include <algorithm>
#include <vector>

using namespace std;

const int N = 1e4+10;
vector<int> vec[N]; 
int book[N]; 

int main()
{
	int n,m; 
	int u,v,ans = 0 ; 
	
	cin>>n>>m; 
	for ( int i=0; i<m; i++ )	 
	{
		scanf("%d%d",&u,&v) ;
		vec[u].push_back(v);
		vec[v].push_back(u); 
	}
	
	for ( int i=1; i<=n; i++ ) 
	{
		book[i] = 1; 
		for ( int j=0; j<vec[i].size(); j++ ) {
			int to1 = vec[i][j]; 
			book[to1] = 1; 
			for ( int l = 0; l<vec[to1].size(); l++ ) {
				int to2 = vec[to1][l]; 
				if ( book[to2]==0 ) ans += vec[to2].size()-1; 
			}
			book[to1] = 0; 
		}
		book[i] = 0; 
	}
	cout<<ans<<endl; 
	return 0; 
}