HDU 1068 Girls and Boys (二分图最大独立集)

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 using namespace std;
 5 const int N = 1e3 + 5;
 6 struct Edge {
 7     int next , to;
 8 }edge[N * N];
 9 int head[N] , cnt;
10 int match[N];
11 bool vis[N];
12 
13 void init() {
14     memset(head , -1 , sizeof(head));
15     memset(match , -1 , sizeof(match));
16     memset(vis , false , sizeof(vis));
17     cnt = 0;
18 }
19 
20 inline void add(int u , int v) {
21     edge[cnt].next = head[u];
22     edge[cnt].to = v;
23     head[u] = cnt++;
24 }
25 
26 bool dfs(int u) {
27     for(int i = head[u] ; ~i ; i = edge[i].next) {
28         int v = edge[i].to;
29         if(!vis[v]) {
30             vis[v] = true;
31             if(match[v] == -1 || dfs(match[v])) {
32                 match[v] = u;
33                 return true;
34             }
35         }
36     }
37     return false;
38 }
39 
40 int hungry(int n) {
41     int res = 0;
42     for(int i = 0 ; i < n ; ++i) {
43         memset(vis , false , sizeof(vis));
44         if(dfs(i))
45             res++;
46     }
47     return res;
48 }
49 
50 int main()
51 {
52     int n;
53     while(~scanf("%d" , &n)) {
54         init();
55         int v;
56         for(int i = 0 ; i < n ; ++i) {
57             int num1 , num;
58             scanf("%d: (%d) ", &num1 , &num);
59             while(num--) {
60                 scanf("%d" , &v);
61                 add(i , v);
62             }
63         }
64         printf("%d\n" , n - hungry(n)/2);
65     }
66     return 0;
67 }