poj2594TreasureExploration(有向图路径可相交的最小路径覆盖)

 
 1 #include
 2 #include
 3 #include
 4 #include
 5 #define N 505
 6 using namespace std;
 7 
 8 int g[N][N];
 9 int n, m;
10 int vis[N], linker[N];
11 bool dfs(int u){
12    for(int i=1; i<=n; ++i)
13       if(g[u][i] && !vis[i]){
14           vis[i]=1;
15           if(!linker[i] || dfs(linker[i])){
16               linker[i]=u;
17               return true;              
18           }
19       }
20    return false;
21 }
22 
23 int main(){
24    while(scanf("%d%d", &n, &m) && (n||m)){
25        memset(g, 0, sizeof(g));
26        while(m--){
27           int u, v;
28           scanf("%d%d", &u, &v);
29           g[u][v]=1;           
30        }                    
31        for(int k=1; k<=n; ++k)
32           for(int i=1; i<=n; ++i)
33              for(int j=1; j<=n; ++j)
34                if(!g[i][j])
35                   g[i][j]=g[i][k]&&g[k][j];
36        memset(linker, 0, sizeof(linker));
37        int ans=0;
38        for(int i=1; i<=n; ++i){
39            memset(vis, 0, sizeof(vis));
40            if(dfs(i))  ++ans;        
41        }
42        printf("%d\n", n-ans);
43    }
44    return 0;    
45 }