PKU 3687 Labeling Balls
#include<iostream>
#include<vector>
using namespace std;
vector<int>adj[5100];
int mark[5100];
int low[5100];
int sstack[5100],stop;
int dfn;
int ans=0;
int bcc[5100],bid;
int degree[5100];
int dfs(int k,int p)
{
int i,j;
low[k]=mark[k]=dfn++;
sstack[stop++]=k;
for(i=0;i<adj[k].size();++i)
{
j=adj[k][i];
if(mark[j]==0)
{
dfs(j,k);
low[k]=min(low[k],low[j]);
}
else if(j!=p)
low[k]=min(low[k],mark[j]);
}
if(mark[k]>low[k])
return 0;
while(sstack[--stop]!=k)
bcc[sstack[stop]]=bid;
bcc[k]=bid;
++bid;
return 0;
}
bool check(int i,int j)
{
int k;
for(k=0;k<adj[i].size();++k)
if(adj[i][k]==j)return false;
return true;
}
int main()
{
int i,j,k;
int n,m;
scanf("%d%d",&n,&m);
for(k=0;k<m;++k)
{
scanf("%d%d",&i,&j);
if(check(i,j))
{
adj[i].push_back(j);
adj[j].push_back(i);
}
}
dfn=1;
bid=1;
stop=0;
memset(mark,0,sizeof(mark));
memset(degree,0,sizeof(degree));
dfs(1,-1);
ans=0;
for(i=1;i<=n;++i)
for(j=0;j<adj[i].size();++j)
if(bcc[i]!=bcc[adj[i][j]])
++degree[bcc[i]];
for(i=1;i<=bid;++i)
if(degree[i]==1)
++ans;
printf("%d\n",(ans+1)/2);
return 0;
}
#include<vector>
using namespace std;
vector<int>adj[5100];
int mark[5100];
int low[5100];
int sstack[5100],stop;
int dfn;
int ans=0;
int bcc[5100],bid;
int degree[5100];
int dfs(int k,int p)
{
int i,j;
low[k]=mark[k]=dfn++;
sstack[stop++]=k;
for(i=0;i<adj[k].size();++i)
{
j=adj[k][i];
if(mark[j]==0)
{
dfs(j,k);
low[k]=min(low[k],low[j]);
}
else if(j!=p)
low[k]=min(low[k],mark[j]);
}
if(mark[k]>low[k])
return 0;
while(sstack[--stop]!=k)
bcc[sstack[stop]]=bid;
bcc[k]=bid;
++bid;
return 0;
}
bool check(int i,int j)
{
int k;
for(k=0;k<adj[i].size();++k)
if(adj[i][k]==j)return false;
return true;
}
int main()
{
int i,j,k;
int n,m;
scanf("%d%d",&n,&m);
for(k=0;k<m;++k)
{
scanf("%d%d",&i,&j);
if(check(i,j))
{
adj[i].push_back(j);
adj[j].push_back(i);
}
}
dfn=1;
bid=1;
stop=0;
memset(mark,0,sizeof(mark));
memset(degree,0,sizeof(degree));
dfs(1,-1);
ans=0;
for(i=1;i<=n;++i)
for(j=0;j<adj[i].size();++j)
if(bcc[i]!=bcc[adj[i][j]])
++degree[bcc[i]];
for(i=1;i<=bid;++i)
if(degree[i]==1)
++ans;
printf("%d\n",(ans+1)/2);
return 0;
}