poj 3895 Cycles of Lanes(DFS找最大环)

#include<iostream>
#include<vector>
#define N 5000
using namespace std;

int vis
,n,m;
int Max;
vector <int> graph
;//vector存储相连接的点

void DFS(int v,int d)
{
vis[v]=d;
int size=graph[v].size();
for(int i=0;i<size;i++)
{
if(!vis[graph[v][i]])//
DFS(graph[v][i],d+1);
else
{
if(vis[v]-vis[graph[v][i]]+1>Max)
Max=vis[v]-vis[graph[v][i]]+1;
}
}
}

int main()
{
int t;
scanf("%d",&t);
while(t--)
{
int s,e;
scanf("%d%d",&n,&m);
for(int i=0;i<=n;i++)
graph[i].clear();

for(int j=0;j<m;j++)
{
scanf("%d%d",&s,&e);
graph[s].push_back(e);
graph[e].push_back(s);
//双向建图
}
Max=0;
memset(vis,0,sizeof(vis));
for(int k=1;k<=n;k++)
{
if(!vis[k])
DFS(k,1);//DFS找环,
}
if(Max<=2)//Max<=2即不存在环
Max=0;
printf("%d\n",Max);
}
return 0;
}