POJ 3660 （Floyd判断传递闭包）

#include <iostream>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <map>
#include <iomanip>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
#include <vector>
//const int maxn = 1e5+5;
#define ll long long
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
//const int inf = 0x6fffffff;

#define MAX INT_MAX
#define FOR(i,a,b) for( int i = a;i <= b;++i)
#define bug cout<<"--------------"<<endl
using namespace std;
bool d[310][310];
int n,m,ans;
int main()
{
      ios::sync_with_stdio(false);
    cin>>n>>m;
    FOR(i,1,n) d[i][i] = 1;
    FOR(i,1,m)
    {
        int x,y,z;
        cin>>x>>y;
        d[x][y] = 1;
    }
    FOR(k,1,n)
    FOR(i,1,n)
    FOR(j,1,n)
    d[i][j] |= d[i][k] & d[k][j];
    for(int i=1 ; i<=n;++i)
    {
        int du = 0;
        for(int j=1;j<=n;++j)
        {
            if(i == j) continue;
            if(d[i][j] == 1 || d[j][i] == 1) du++;
        }
        if(du == n-1) ans++;
    }
    cout<<ans<<endl;
}