zju1085Alien Security

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=85

zju Alien Security     spfa
#include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<queue>
using namespace std;
const int INF=1000000;
int vis[101],g[101][101],d[101];
int n,ET;//ET目标房间
void spfa()//Bellman_Ford的队列实现，求单源点最短路径
{ 
	
     queue<int > q;
	 bool inq[101];
	 for(int i=0;i<n;i++)d[i]=(i==ET?0:INF);
	 memset(inq,0,sizeof(inq));
	 q.push(ET);
	 while(!q.empty())
	 {
		 int t=q.front();q.pop();
		 inq[t]=false;
		 for(int i=0;i<n;i++)//一般用邻接链表
		 {
			 if(g[i][t]&&d[i]>d[t]+1)
			 {
				 d[i]=d[t]+1; 
				 if(!inq[i])
				 {
					 inq[i]=1;
					 q.push(i);
				 }
			 }
		 }
	 }
}
bool BFS(int x)//假设x去掉，是否能从起点到终点，即x是否为必经之点
{
	memset(vis,0,sizeof(vis));
     queue <int> q;
	 q.push(0);
	 vis[0]=1;
	 while(!q.empty())
	 {
		 int t=q.front();
		 q.pop();
		 if(t==ET)return 0;
		 for(int i=0;i<n;i++)
		 {
			 if(!vis[i]&&g[t][i]&&i!=x)
			 {
				 vis[i]=1;
				 q.push(i);
			 }
		 }
	 }
	 return 1;
}
int main()
{
	int cas;
	string s;
	cin>>cas;
	while(cas--)
	{
		memset(g,0,sizeof(g));
		cin>>n>>ET;//此乃变态输入
		getline(cin,s);
		for(;;)
		{
			if(getline(cin,s)==0||s=="")break;
			int a=s[0]-'0',b=s[2]-'0';
			g[a][b]=1;
		}
		spfa();
		int ans=INF,ANS=-1;
		for(int i=0;i<n;i++)
		{
			if(i!=ET&&BFS(i))//如果i为必经点
			{
				if(d[i]<ans){ans=d[i];ANS=i;}
			}			
		}
		if(ANS==-1)cout<<"Put guards in room 0."<<endl;
		else cout<<"Put guards in room "<<ANS<<"."<<endl;
		if(cas)cout<<endl;
	}
}