```cpp
// luogu-judger-enable-o2
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <iostream>
#include <vector>
#include <queue>
#include <bitset>
#define maxn 1005
std::vector<int> G[maxn]; // positive , negetive
int n , m , ans , d[maxn];
bool vis[maxn][maxn];
std::bitset<maxn> s[maxn];
inline void Toposort()
{
std::queue<int> q;
for(int i = 1 ; i <= n ; ++i)
if(!d[i]) q.push(i);
while(!q.empty())
{
int k = q.front();
q.pop();
for(int i = 0 ; i < (int)G[k].size() ; ++i){
int v = G[k][i];
s[v] |= s[k];
--d[v];
if(!d[v]) q.push(v);
}
}
}
int main()
{
// freopen("Bitset.in","r",stdin);
// freopen("my.out","w",stdout);
scanf("%d%d",&n,&m);
printf("%d %d\n",n,m);
for(int i = 1 ; i <= m ; ++i){
int x , y;
scanf("%d%d",&x,&y);
// if(vis[x][y] || vis[y][x]) continue;
G[y].push_back(x);
// vis[x][y] = vis[y][x] = true;
++d[x];
}
for(int i = 1 ; i <= n ; ++i)
s[i] |= (1 << i);
Toposort();
// for(int i = 1 ; i <= n ; ++i)
// printf("%d ",s[i].count());
for(int i = 1 ; i <= n ; ++i)
ans += s[i].count();//include itself , so it is n
ans = n * (n + 1) / 2 - ans;
printf("%d",ans);
}
```
by Starrydream @ 2018-11-03 16:43:25
可能这个题有环？
by Starrydream @ 2018-11-03 17:04:37