hdu 3836 Equivalent Sets

http://www.cppblog.com/sosi/archive/2010/09/26/127797.aspx

tarjan算法

#include<iostream>
#include<vector>
#include<stack>
#define maxn 20005
using namespace std;
int n,m;
int t,point;
struct stu
{
	int visit;
	int dfn;
	int low;
	int instack;
	int root;
	void init()
	{
		root=-1;
		dfn=-1;
		visit=0;
		low=-1;
		instack=0;
	}
};
vector<int>mapp[maxn];
stack<int>s;
stu h[maxn];
int head[maxn],nextt[maxn];
void init()
{
	for(int i=0;i<maxn;i++) mapp[i].clear(),head[i]=0,nextt[i]=0,h[i].init();
	while(s.size()) s.pop();
	t=1;
	point=1;
}
void input()
{
	for(int i=0;i<m;i++)
	{
		int x,y;
		cin>>x>>y;
		mapp[x].push_back(y);
	}
}
void tarjan(int x)
{
	s.push(x);
	h[x].visit=1;
	h[x].dfn=t++;
	h[x].instack=1;
	h[x].low=h[x].dfn;
	for(int i=0;i<mapp[x].size();i++)
	{
		if(!h[mapp[x][i]].visit)
		{
			tarjan(mapp[x][i]);
			h[x].low=min(h[x].low,h[mapp[x][i]].low);
		}
		else if(h[mapp[x][i]].instack) h[x].low=min(h[x].low,h[mapp[x][i]].dfn);
	}
	if(h[x].dfn==h[x].low)
	{
		int w;
		do
		{
			w=s.top();
			h[w].root=point;
			h[w].instack=0;
			s.pop();
		}while(w!=x);
		point++;
	}
}
int main()
{
	while(cin>>n>>m)
	{
		init();
		input();
		for(int i=1;i<=n;i++)
		{
			if(!h[i].visit) tarjan(i);
		}
		for(int i=1;i<=n;i++)
		{
			for(int j=0;j<mapp[i].size();j++)
			{
				if(h[mapp[i][j]].root!=h[i].root) nextt[h[i].root]++,head[h[mapp[i][j]].root]++;
			}
		}
		int in=0,out=0;
		for(int i=1;i<point;i++)
		{
			if(!head[i]) in++;
			if(!nextt[i]) out++;
		}
		if(point==2) cout<<"0"<<endl;
		else cout<<max(in,out)<<endl;
	}
	return 0;
}