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 = 1005;
int n, m;
bitset<maxn> maps[maxn];
void floyd() {
    for (int k = 1; k <= n; k++) {
        for (int i = 1; i <= n; i++) {
            if (maps[i][k]) maps[i] |= maps[k];
        }
    }
}
int main() {
    scanf("%d%d",&n,&m);
    for (int i = 1; i <= m; i++) {
        int u, v; scanf("%d%d",&u,&v);
        maps[u][v] = true;
    }
    floyd();
    int ans = 0;
    for (int i = 1; i <= n; i++) {
        for (int j = i+1; j <= n; j++) {
            if (!maps[i][j] && !maps[j][i]) ans++;
        }
    }
    printf("%d\n",ans);
    return 0;
}