poj 3660 传递闭包

#include <iostream>
using namespace std;
const int maxn=105;

bool f[maxn][maxn];
int b[maxn];
int n,m,ans;
int main()
{
int i,j,k;
scanf("%d%d",&n,&m);
for (i=0;i<m;i++)
{
int x,y;
scanf("%d%d",&x,&y);
f[x][y]=true;
}
for (k=1;k<=n;k++)
for (i=1;i<=n;i++)
for (j=1;j<=n;j++)
f[i][j]=f[i][j] || f[i][k] && f[k][j];
for (i=1;i<=n;i++)
for (j=1;j<=n;j++)
if (f[i][j] || f[j][i])
b[i]++;
ans=0;
for (i=1;i<=n;i++)
if (b[i]==n-1) ans++;
cout << ans << endl;
}