POJ3275 Ranking the Cows floyd的bitset优化

POJ3275 Ranking the Cows

 #include <iostream>
 #include <cstdio>
 #include <bitset>
 using namespace std;
 const int maxn = ;
 int n, m;
 bitset<maxn> maps[maxn];
 void floyd() {
     for (int k = ; k <= n; k++) {
         for (int i = ; i <= n; i++) {
             if (maps[i][k]) maps[i] |= maps[k];
         }
     }
 }
 int main() {
     scanf("%d%d",&n,&m);
     for (int i = ; i <= m; i++) {
         int u, v; scanf("%d%d",&u,&v);
         maps[u][v] = true;
     }
     floyd();
     int ans = ;
     for (int i = ; i <= n; i++) {
         for (int j = i+; j <= n; j++) {
             if (!maps[i][j] && !maps[j][i]) ans++;
         }
     }
     printf("%d\n",ans);
     return ;
 }