HDOJ 5154 Harry and Magical Computer floyd判环

 floyd判环

Harry and Magical Computer

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1005    Accepted Submission(s): 404

Problem Description

In reward of being yearly outstanding magic student, Harry gets a magical computer. When the computer begins to deal with a process, it will work until the ending of the processes. One day the computer got n processes to deal with. We number the processes from 1 to n. However there are some dependencies between some processes. When there exists a dependencies (a, b), it means process b must be finished before process a. By knowing all the m dependencies, Harry wants to know if the computer can finish all the n processes.

 

Input

There are several test cases, you should process to the end of file.
For each test case, there are two numbers n m on the first line, indicates the number processes and the number of dependencies.  1≤n≤100,1≤m≤10000
The next following m lines, each line contains two numbers a b, indicates a dependencies (a, b).  1≤a,b≤n

 

Output

Output one line for each test case. 
If the computer can finish all the process print "YES" (Without quotes).
Else print "NO" (Without quotes).

 

Sample Input

   
   
   
   

    
    
    
    3 2
3 1
2 1
3 3
3 2
2 1
1 3
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    YES
NO
   
   
   
   

 

Source

BestCoder Round #25

 

/* ***********************************************
Author        :CKboss
Created Time  :2015年02月15日 星期日 22时23分31秒
File Name     :HDOJ5154.cpp
************************************************ */

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <cstdlib>
#include <vector>
#include <queue>
#include <set>
#include <map>

using namespace std;

const int maxn=110;
const int INF=0x3f3f3f3f;

int n,m;
int g[maxn][maxn];

int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);

	while(scanf("%d%d",&n,&m)!=EOF)
	{
		memset(g,63,sizeof(g));
		for(int i=0;i<m;i++)
		{
			int a,b;
			scanf("%d%d",&a,&b);
			g[a][b]=1;
		}

		for(int k=1;k<=n;k++)
			for(int i=1;i<=n;i++)
				for(int j=1;j<=n;j++)
					g[i][j]=min(g[i][j],g[i][k]+g[k][j]);

		bool flag=false;
		for(int i=1;i<=n;i++)
		{
			for(int j=1;j<=n;j++)
			{
				if(g[i][j]==g[j][i]&&g[i][j]!=INF)
				{
					flag=true;
					break;
				}
			}
			if(flag) break;
		}
		if(flag) puts("NO");
		else puts("YES");
	}
    
    return 0;
}