bzoj1703[Usaco2007 Mar]Ranking the Cows 奶牛排名

大水题，明显传递闭包，直接bitset优化即可，随手1A= =

#include<cstdio>#include<cstring>#include<algorithm>#include<bitset>#define fo(i,a,b) for(int i=a;i<=b;i++)#define fd(i,a,b) for(int i=a;i>=b;i--)using namespace std;const int N=1e3+5;int n,m;bitset<N> a[N]; int main(){    scanf("%d%d",&n,&m);    fo(i,1,m)    {        int x,y;        scanf("%d%d",&x,&y);        a[x][y]=1;     }    fo(i,1,n)    fo(j,1,n)    if (a[j][i])a[j]|=a[i];    int ans=0;    fo(i,1,n)    fo(j,i+1,n)    if (!a[i][j]&&!a[j][i])ans++;    printf("%d\n",ans);}