hlg1492盒子【最小路径覆盖】

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 using namespace std;
 5 
 6 const int maxn = 505;
 7 
 8 struct Node {
 9     int to;
10     int next;
11 }p[maxn * maxn];
12 int head[maxn * maxn];
13 int tot;
14 void AddEdge(int u, int v) {
15     p[tot].to = v;
16     p[tot].next = head[u];
17     head[u] = tot++;
18 }
19 
20 int Link[maxn];
21 int vis[maxn];
22 
23 bool Find(int u) {
24     for(int i = head[u]; i; i = p[i].next) {
25         int v = p[i].to;
26         if(!vis[v]) {
27             vis[v] = 1;
28             if(Link[v] == -1 || Find(Link[v])) {
29                 Link[v] = u;
30                 return true;
31             }
32         }
33     }
34     return false;
35 }
36 
37 int solve(int n) {
38     int cnt = 0;
39     memset(Link, -1, sizeof(Link));
40     for(int i = 1; i <= n; i++) {
41         memset(vis, 0, sizeof(vis));
42         if(Find(i)) {
43             cnt++;
44         }
45     }
46     return cnt;
47 }
48 
49 int main() {
50     int n, m;
51     int u, v;
52     while(EOF != scanf("%d %d",&n, &m)) {
53         memset(head, 0, sizeof(head));
54         tot = 1;
55         for(int i = 0; i < m; i++) {
56             scanf("%d %d",&u, &v);
57             AddEdge(u, v);
58         }
59         printf("%d\n",n - solve(n));
60     }
61     return 0;
62 }