记录编号	421746	评测结果	AAAAAAATTT
题目名称	[HAOI 2016]食物链	最终得分	70
用户昵称	@@2@	是否通过	未通过
代码语言	C++	运行时间	3.128 s
提交时间	2017-07-08 08:58:12	内存使用	24.15 MiB

#include <algorithm>
#include <fstream>
#include <vector>
#include <queue>
#include <cstdlib>
using namespace std;
ifstream cin("chain_2016.in");
ofstream cout("chain_2016.out");
vector<int> e1[1000001]; //1 -> 2
vector<int> e2[1000001]; //2 -> 1
vector<int> end;
bool note[1000001];
int n,m;
queue<int> start;
int ans = 0;
int bfs()
{
	start.size();
	while(!start.empty())
	{
		int h = start.front();
		start.pop();

			if (note[h] == 1)
			{
				ans++;
				/* code */
			}

		for (int i = 0; i != e1[h].size(); ++i)
		{
			start.push(e1[h][i]);
		}
	}
}
int main() 
{
	int i,j,k,t1,t2;
	cin >> n >> m;
	for (i = 1; i <= m; ++i)
	{
		cin >> t1 >> t2;
		e1[t1] .push_back(t2);
		e2[t2] .push_back(t1);
	}
	for (i = 1; i <= n; ++i)
	{
		if(e2[i].size() == 0)
		{
			if(!(e1[i].size() == 0&&e2[i].size() == 0))
				start.push(i);
		}
		if(e1[i].size() == 0)
		{
			//end.push_back(i);
			note[i] = 1;
		}
	}

	bfs();
	cout << ans << endl;
	cin.close();				
	cout.close();
		return 0;
}