POJ3275 Ranking the Cows
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 }
