OJ-Problems-Source/HDOJ/2767_autoAC.cpp

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#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <stack>
using namespace std;
#define MAXN 200010
#define clr(x,k) memset((x),(k),sizeof(x))
struct node
{
int st,to,next;
}
edge[MAXN];
int n,m,ct,id;
int head[MAXN],low[MAXN],dfn[MAXN],belong[MAXN],in[MAXN],to[MAXN];
bool instack[MAXN];
stack<int>q;
void add_e(int i,int u,int v)
{
edge[i].st=u;
edge[i].to=v;
edge[i].next=head[u];
head[u]=i;
}
void tarjan(int i)
{
int j;
dfn[i]=low[i]=++id;
q.push(i);
instack[i]=1;
for(int u=head[i]; ~u; u=edge[u].next)
{
j=edge[u].to;
if(dfn[j]==0)
{
tarjan(j);
if(low[i]>low[j])
low[i]=low[j];
}
else if(instack[j]&&low[i]>low[j])
low[i]=dfn[j];
}
if(dfn[i]==low[i])
{
ct++;
do
{
j=q.top();
q.pop();
instack[j]=0;
belong[j]=ct;
}
while(i!=j);
}
}
int main()
{
int t,i,u,v,sum1,sum2;
cin>>t;
while(t--)
{
clr(head,-1);
clr(low,0);
clr(dfn,0);
clr(belong,0);
clr(in,0);
clr(to,0);
while(!q.empty())
q.pop();
cin>>n>>m;
for(i=0; i<m; i++)
{
cin>>u>>v;
add_e(i,u,v);
}
id=ct=0;
for(i=1; i<=n; i++)
{
if(!dfn[i])
tarjan(i);
}
if(ct==1)
{
cout<<0<<endl;
continue;
}
for(i=1; i<=ct; i++)
{
in[i]=to[i]=0;
}
for(i=0; i<m; i++)
{
if(belong[edge[i].st]!=belong[edge[i].to])
{
in[belong[edge[i].st]]++;
to[belong[edge[i].to]]++;
}
}
sum1=sum2=0;
for(i=1; i<=ct; i++)
{
if(in[i]==0)
sum1++;
if(to[i]==0)
sum2++;
}
cout<<max(sum1,sum2)<<endl;
}
return 0;
}