[POJ3041] Asteroids（最小点覆盖-匈牙利算法）

 1 #include <cstdio>
 2 #include <cstring>
 3 #define M(x, a) memset(a, x, sizeof(a))
 4 
 5 using namespace std;
 6 
 7 const int MAXN = 501;
 8 int n, k, cnt, ans;
 9 int head[MAXN], next[MAXN * MAXN], to[MAXN * MAXN], belong[MAXN];
10 bool vis[MAXN];
11 
12 inline void add(int x, int y)
13 {
14     to[cnt] = y;
15     next[cnt] = head[x];
16     head[x] = cnt++;
17 }
18 
19 inline bool find(int u)
20 {
21     int i, v;
22     for(i = head[u]; i != -1; i = next[i])
23     {
24         v = to[i];
25         if(!vis[v])
26         {
27             vis[v] = 1;
28             if(!belong[v] || find(belong[v]))
29             {
30                 belong[v] = u;
31                 return 1;
32             }
33         }
34     }
35     return 0;
36 }
37 
38 int main()
39 {
40     int i, x, y;
41     scanf("%d %d", &n, &k);
42     M(-1, head);
43     for(i = 1; i <= k; i++)
44     {
45         scanf("%d %d", &x, &y);
46         add(x, y);
47     }
48     for(i = 1; i <= n; i++)
49     {
50         M(0, vis);
51         if(find(i)) ans++;
52     }
53     printf("%d", ans);
54     return 0;
55 }