拓扑排序 2892. Task

Peter is very interested in Artificial Intelligence. His teacher leaves him several problems. Since he is not very familiar with the subject, he will read some necessary information to complete the task. But unfortunately there are some constrains between the problems (that one problem must be done after another one). Please write a program to judge whether Peter can complete the task.

Input

There are several test cases in the input data. The first line contains the number of test cases. In each test case, the first line contains two positive integers n (1 ≤ n ≤ 20) and m (0 ≤ m ≤ 20), denoting that there are n problems and m constrains. Then there are m lines to describe the constrains, and each line contains two different integers i and j (1 ≤ i, j ≤ n), denoting that the problem j must be done after the problem i. (The problems' number starts at 1.)

Output

Please write a program to judge whether Peter can complete the task. If he can, please output "1"; otherwise output "0" instead.

Sample Input

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

Sample Output

1
0

#include<iostream>
#include<cstring>
#include<stack>
using namespace std;
int map[21][21],degree[21];
int main(){
	int t,m,n,count,a,b;
	cin>>t;
	while(t--)
	{
		cin>>n>>m;
		memset(map,0,sizeof(map));
		memset(degree,0,sizeof(degree));
		for(int i=1;i<=m;i++)
		{
			cin>>a>>b;
			map[a][b]=1;
			degree[b]++;
		}
		stack<int>s;
		for(int i=1;i<n;i++)
		{
			if(degree[i]==0)
				s.push(i);
		}
		if(s.empty())
		{
			cout<<"0"<<endl;
			continue;
		}
		count=0;
		while(!s.empty())
		{
			int temp=s.top();
			s.pop();
			count++;
			for(int i=1;i<=n;i++)
			{
				if(map[temp][i])
				{
					degree[i]--;
					if(degree[i]==0)
						s.push(i);
				}
			}
		}
		if(count==n)
			cout<<"1"<<endl;
		else
			cout<<"0"<<endl;
	}
	return 0;
}