POJ 3660 Cow Contest

# include <cstdio>
# include <iostream>
# include <cstring>
# include <vector>

# define N 105

using namespace std;

int n, m;
char vis
;
vector <int> pre
;
vector <int> aft
;

int bfs(int u, int d)
{
int i, ret, cx, nx, front, rear, size;
int Q[1000*N];

Q[1] = u;
memset(vis, 0, sizeof(vis));
vis[u] = 1;

front = 1;
rear  = 2;

ret = 0;
while (front < rear)
{
cx = Q[front++];
size = d>0 ? aft[cx].size():pre[cx].size();
for (i = 0; i < size; ++i)
{
nx = d>0 ? aft[cx][i]:pre[cx][i];
if (!vis[nx])
{
Q[rear++] = nx;
vis[nx] = 1;
++ret;
}
}
}

return ret;
}

int main()
{
int i, cnt, u, v;

while (~scanf("%d%d", &n, &m))
{
for (i = 1; i <= n; ++i)
{
pre[i].clear();
aft[i].clear();
}
for (i = 0; i < m; ++i)
{
scanf("%d%d", &u, &v);
pre[v].push_back(u);
aft[u].push_back(v);
}
cnt = 0;
for (i = 1; i <= n; ++i)
{
if (bfs(i, 1)+bfs(i, -1) == n-1) ++cnt;
}
printf("%d\n", cnt);
}

return 0;
}