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);
}
}