记录编号	449214	评测结果	RRRRRRRRRR
题目名称	[Codeforces 819A] B先生和无聊的游戏	最终得分	0
用户昵称	@@@	是否通过	未通过
代码语言	C++	运行时间	0.004 s
提交时间	2017-09-13 21:18:39	内存使用	0.60 MiB

#include <fstream>
#include <vector>
#include <queue>
#include <time.h>
using namespace std;
ifstream cin("roadb.in");
ofstream cout("roadb.out");

int n,m,s,t;
int d[10005];
bool book[10005],path[10005];
vector<int> v[10005],vv[10005];
queue<int> q;

void bfs()
{
	for(int i = 1;i <= n;i++)
	{
		book[i] = 1;
	}
	queue<int> qq;
	qq.push(t);
	path[t] = 1;
	while(!qq.empty())
	{
		int h = qq.front();
		qq.pop();
		for(int i = 0;i < vv[h].size();i++)
			if(path[vv[h][i]] == 0)
		{
			path[vv[h][i]] = 1;
			book[vv[h][i]] = 0;
			qq.push(vv[h][i]);
		}
	}

}
bool c(int x)
{
	for(int i = 0;i < v[x].size();i++)
	{
		if(book[v[x][i]] == 1)
			return 0;
	}
	return 1;
}
void dj()
{
	int i,j,k,h;
	for(i = 1;i <= n;i++)
	{
		d[i] = 999999999;
	}
	book[t] = 0;
	d[s] = 0;
	q.push(s);
	book[s] = 1;
	while(!q.empty())
	{
		h = q.front();
		q.pop();
		book[h] = 0;
		for(i = 0;i < v[h].size();i++)
		{
			if(book[v[h][i]] == 0)
				if(c(v[h][i]))
			if(d[v[h][i]] > d[h]+1)
			{
				book[v[h][i]] = 1;
				d[v[h][i]] = d[h]+1;
				
				q.push(v[h][i]);
			}
		}
	}
	
	
	
}

int cyf()
{	
	int i,j,k;
	cin >> n >> m;
	for(i = 1;i <= m;i++)
	{
		int t1,t2;
		cin >> t1 >> t2;
		if(t1 != t2)
		v[t1].push_back(t2);
		vv[t2].push_back(t1);
		
	}
	cin >> s >> t;
	bfs();
	dj() ;
	if(d[t] == 999999999)
	{
		cout << -1 << endl;
	}
	else
	{
		cout << d[t] << endl;
	}
	cin.close();	
	cout.close();
	return 0;
}
int hhhh = cyf();
int main() {;}