学步园

Tarjan真NB，强连通分量，割点，桥，点双连通分量，边双连通分量，LCA都有Tarjan的身影，这么多东西还有很多不懂的地方...

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<stack>
#include<fstream>
using namespace std;
#define maxv 10005
vector<int> E[maxv],V[maxv],NE[maxv];
stack<int> Stack;
int DFN[maxv],LOW[maxv];
bool Instack[maxv];
int Index,Cnt,Out[maxv],Belong[maxv];
void Init_Tarjan()
{
    int i;
    for(i=1;i<=maxv;++i)
        V[i].clear(),NE[maxv].clear();
    while(!Stack.empty())
        Stack.pop();
    memset(DFN,0,sizeof(DFN));
    memset(LOW,0,sizeof(LOW));
    memset(Instack,false,sizeof(Instack));
    Cnt=Index=0;
    memset(Out,0,sizeof(Out));
}
void Tarjan(int u)
{
    DFN[u]=LOW[u]=++Index;
    Stack.push(u);
    Instack[u]=true;
    int v,i;
    for(i=0;i<E[u].size();++i)
    {
        v=E[u][i];
        if(DFN[v]==0)
        {
            Tarjan(v);
            LOW[u]=min(LOW[u],LOW[v]);
        }
        else if(Instack[v])
            LOW[u]=min(LOW[u],DFN[v]);
    }
    if(DFN[u]==LOW[u])
    {
        Cnt++;
        do{
        v=Stack.top();
        Stack.pop();
        Instack[v]=false;
        V[Cnt].push_back(v);
        Belong[v]=Cnt;
        }while(v!=u);
    }
}
int Create_New_Graph()
{
    int i,j,k,v,cnt,ans;
    bool in[maxv];
    for(i=1;i<=Cnt;++i)
    {
        memset(in,false,sizeof(in));
        for(j=0;j<V[i].size();++j)
        {
            for(k=0;k<E[V[i][j]].size();++k)
            {
                v=E[V[i][j]][k];
                in[Belong[v]]=true;
            }
        }
        in[i]=false;
        cnt=0;
        for(j=1;j<=Cnt;++j)   
            if(in[j]==true)
                cnt++;
        Out[i]=cnt;
    }
    cnt=0;
    for(i=1;i<=Cnt;++i)
        if(Out[i]==0)
            cnt++,ans=i;
    if(cnt==1)
        return ans;
    else
        return -1;
}     
int main()
{
    int n,m,i,fm,to,ans;
    while(cin>>n>>m)    
    {
        for(i=1;i<=n;++i)
            E[i].clear();
        for(i=1;i<=m;++i)
        {
            cin>>fm>>to;
            E[fm].push_back(to);
        }
        Init_Tarjan();
        for(i=1;i<=n;++i)
            if(DFN[i]==0)
                Tarjan(i);
        ans=Create_New_Graph();
        if(ans==-1)
            cout<<0<<endl;
        else
            cout<<V[ans].size()<<endl;
    }
    return 0;
}