POJ2594 Treasure Exploration

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstdlib>
 4 #include <cstring>
 5 
 6 inline void read(int &x)
 7 {
 8     x = 0;char ch = getchar(), c = ch;
 9     while(ch < ‘0‘ || ch > ‘9‘)c = ch, ch = getchar();
10     while(ch <= ‘9‘ && ch >= ‘0‘)x = x * 10 + ch - ‘0‘, ch = getchar();
11     if(c == ‘-‘)x = -x;
12 }
13 
14 const int INF = 0x3f3f3f3f;
15 
16 struct Edge
17 {
18     int u,v,next;
19     Edge(int _u, int _v, int _next){u = _u, v = _v, next = _next;}
20     Edge(){}
21 }edge[250010];
22 
23 int head[510], cnt;
24 
25 inline void insert(int a, int b)
26 {
27     edge[++cnt] = Edge(a,b,head[a]);
28     head[a] = cnt;
29 }
30 
31 int n,m,lk[510],b[510],g[510][610];
32 
33 int dfs(int u)
34 {
35     for(register int pos = head[u];pos;pos = edge[pos].next)
36     {
37         int v = edge[pos].v;
38         if(b[v])continue;
39         b[v] = 1;
40         if(lk[v] == -1 || dfs(lk[v]))
41         {
42             lk[v] = u;
43             return 1;
44         }
45     }
46     return 0;
47 }
48 
49 int xiongyali()
50 {
51     int ans = 0;
52     memset(lk, -1, sizeof(lk));
53     for(register int i = 1;i <= n;++ i)
54     {
55         memset(b, 0, sizeof(b));
56         ans += dfs(i);
57     }
58     return ans;
59 }
60 
61 int main()
62 {
63     while(scanf("%d %d", &n, &m) != EOF && (n + m))
64     {
65         memset(edge, 0, sizeof(edge));
66         memset(head, 0, sizeof(head));
67         memset(g, 0, sizeof(g));
68         cnt = 0;
69         int tmp1, tmp2;
70         for(register int i = 1;i <= m;++ i)
71         {
72             read(tmp1), read(tmp2);
73             g[tmp1][tmp2] = 1;
74         }
75         for(register int k = 1;k <= n;++ k)
76             for(int i = 1;i <= n;++ i)
77                 for(int j = 1;j <= n;++j)
78                     g[i][j] |= g[i][k] && g[k][j];
79         for(register int i = 1;i <= n;++ i)
80             for(int j = 1;j <= n;++ j)
81                 if(g[i][j]) insert(i, j);
82         printf("%d\n", n - xiongyali());
83     }
84     return 0;
85 }