POJ 2594 传递闭包的最小路径覆盖

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <iostream>
 5 #include <vector>
 6 #include <queue>
 7 #include <cmath>
 8 #include <set>
 9 using namespace std;
10 
11 #define N 505
12 
13 int max(int x,int y){return x>y?x:y;}
14 int min(int x,int y){return x<y?x:y;}
15 int abs(int x,int y){return x<0?-x:x;}
16 
17 int from[N];
18 bool visited[N];
19 int n, m;
20 int map[N][N];
21 
22 int march(int u){
23     int i, v;
24     for(v=1;v<=n;v++){
25         if(!visited[v]&&map[u][v]){
26             visited[v]=true;
27             if(from[v]==-1||march(from[v])){
28                 from[v]=u;
29                 return 1;
30             }
31         }
32     }
33     return 0;
34 }
35 
36 main()
37 {
38     int i, j, k, u, v;
39     while(scanf("%d %d",&n,&m)==2){
40         if(n==0&&m==0) break;
41         memset(map,0,sizeof(map));
42         for(i=0;i<m;i++){
43             scanf("%d %d",&u,&v);
44             map[u][v]=1;
45         }
46         for(i=1;i<=n;i++){
47             for(j=1;j<=n;j++){
48                 for(k=1;k<=n;k++){
49                     if(map[i][j]&&map[j][k]&&!map[i][k]) map[i][k]=1; 
50                 }
51             }
52         }
53         int num=0;
54         memset(from,-1,sizeof(from));
55         for(i=1;i<=n;i++){
56             memset(visited,false,sizeof(visited));
57             if(march(i)) num++;
58         }
59         printf("%d\n",n-num);
60     }
61 }