Tarjan

//-----------Tarjan-------------

int dfn[MAXNODE],low[MAXNODE],index;
int stack[MAXNODE],top;
int id_scc[MAXNODE],cnt_scc;

void Tarjan(int i)
{
    int j;
    dfn[i]=low[i]=++index;
    stack[++top]=i;
    for(Node *p=G[i];p;p=p->next)
    {
        j=p->num;
        if(!dfn[j])
        {
            Tarjan(j);
            if(low[j]<low[i])
                low[i]=low[j];
        }
        else if(!id_scc[j] && dfn[j]<low[i])
            low[i]=dfn[j];
    }
    if(dfn[i]==low[i])
    {
        cnt_scc++;
        do 
        {
            j=stack[top--];
            id_scc[j]=cnt_scc;
        } while (i!=j);
    }
}
void solve(int nodenum)
{
    index=top=cnt_scc=0;
    memset(dfn,0,sizeof(dfn));
    memset(id_scc,0,sizeof(id_scc));
    for(int i=1;i<=nodenum;i++)
    {
        if(!dfn[i])
            Tarjan(i);
    }
}