POJ3275 Ranking the Cows floyd的bitset优化

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <bitset>
 4 using namespace std;
 5 const int maxn = 1005;
 6 int n, m;
 7 bitset<maxn> maps[maxn];
 8 void floyd() {
 9     for (int k = 1; k <= n; k++) {
10         for (int i = 1; i <= n; i++) {
11             if (maps[i][k]) maps[i] |= maps[k];
12         }
13     }
14 }
15 int main() {
16     scanf("%d%d",&n,&m);
17     for (int i = 1; i <= m; i++) {
18         int u, v; scanf("%d%d",&u,&v);
19         maps[u][v] = true;
20     }
21     floyd();
22     int ans = 0;
23     for (int i = 1; i <= n; i++) {
24         for (int j = i+1; j <= n; j++) {
25             if (!maps[i][j] && !maps[j][i]) ans++;
26         }
27     }
28     printf("%d\n",ans);
29     return 0;
30 }