OJ-Problems-Source/HDOJ/3836_autoAC.cpp

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#include"stdio.h"
#include"string.h"
#include"stdlib.h"
#include"stack"
#define N 30000
using namespace std;
int n,m;
int index_s;
int instack[N],DFN[N],LOW[N];
int belong[N],indegree[N],outdegree[N];
struct Eage
{
int from,to,next;
}eage[2*N];
int tot,head[N];
void add(int a,int b)
{
eage[tot].from=a;
eage[tot].to=b;
eage[tot].next=head[a];
head[a]=tot++;
}
void getmap()
{
int i,l;
int a,b;
tot=0;
memset(head,-1,sizeof(head));
while(m--) {scanf("%d%d",&a,&b);add(a,b);}
}
stack<int>st;
void Tarjan(int k)
{
int j,v;
st.push(k);
instack[k]=1;
DFN[k]=LOW[k]=++index_s;
for(j=head[k];j!=-1;j=eage[j].next)
{
v=eage[j].to;
if(instack[v]) LOW[k]=LOW[k]>DFN[v]?DFN[v]:LOW[k];
else if(DFN[v]==-1)
{
Tarjan(v);
LOW[k]=LOW[k]>LOW[v]?LOW[v]:LOW[k];
}
}
if(DFN[k]==LOW[k])
{
do
{
j=st.top();
st.pop();
instack[j]=0;
belong[j]=k;
}while(j!=k);
}
}
void getdegree()
{
int i,l;
memset(indegree,0,sizeof(indegree));
memset(outdegree,0,sizeof(outdegree));
for(i=0;i<tot;i++)
{
if(belong[eage[i].from]==belong[eage[i].to]) continue;
indegree[belong[eage[i].to]]++;
outdegree[belong[eage[i].from]]++;
}
}
int main()
{
int i;
int temp,t1,t2,ans;
while(scanf("%d%d",&n,&m)!=-1)
{
getmap();
index_s=0;
memset(DFN,-1,sizeof(DFN));
memset(LOW,-1,sizeof(LOW));
memset(instack,0,sizeof(instack));
for(i=1;i<=n;i++) if(DFN[i]==-1) Tarjan(i);
getdegree();
temp=t1=t2=0;
for(i=1;i<=n;i++)
{
if(belong[i]!=i) continue;
temp++;
if(indegree[i]==0) t1++;
if(outdegree[i]==0) t2++;
}
ans=t1>t2?t1:t2;
if(n<1 || temp==1) ans=0;
printf("%d\n",ans);
}
return 0;
}