zoj1311Network

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=311

割点算法

《算法与艺术信息学竞赛》P285

建立在DFS的基础上

#include<iostream>
#include<cstring>
#include<vector>
#include<algorithm>
#include<stdio.h>
#include<string>
#include<sstream>
using namespace std;
int n,m,k,ans,d[101],ancestor[101],c[101],cut[101];
vector <int> adj[101];
void DFS(int k,int fa,int deep)
{
	int tot;
    c[k]=-1;
	d[k]=deep;
	ancestor[k]=deep,tot=0;
	for(int i=0;i<adj[k].size();i++)
	{
		int w=adj[k][i];
		if(w!=fa&&c[w]==-1)ancestor[k]=min( ancestor[k], d[w] );
		else if(c[w]==0)
		{
			DFS(w,k,deep+1);
			tot++,ancestor[k]=min(ancestor[k],ancestor[w]);
			if(fa==-1&&tot>1||fa!=-1&&ancestor[w]>=d[k])
				cut[k]=1;
		}	
	}
	c[k]=1;

}
int main()
{
	string s;
     while(cin>>n&&n)
	 {
		
	   for(int i=1;i<=n;i++)
		   adj[i].clear();
       while(getline(cin,s)&&s!="0")
	   {
		   istringstream sin(s);
		   sin>>m;
		   if(m)
		   {
			   while(sin>>k)
			   {
				   adj[k].push_back(m);
				   adj[m].push_back(k);
			   }
		   }
		  
	   }
	   memset(d,0,sizeof(d));
	   memset(c,0,sizeof(c));
	   memset(cut,0,sizeof(cut));
	   memset(ancestor,0,sizeof(ancestor));
	   ans=0;
	   for(int i=1;i<=n;i++)
	   {
		   if(!c[i])DFS(i,-1,0);
	   }
	   for(int i=1;i<=n;i++)
		   if(cut[i])ans++;
	   printf("%d\n",ans);

	 }
}