poj 2594Treasure Exploration(有向图路径可相交的最小路径覆盖)

 
 1 #include<iostream>
 #include<cstring>
 #include<algorithm>
 #include<cstdio>
 #define N 505
 using namespace std;

 int g[N][N];
 int n, m;
 int vis[N], linker[N];
 bool dfs(int u){
    for(int i=; i<=n; ++i)
       if(g[u][i] && !vis[i]){
           vis[i]=;
           if(!linker[i] || dfs(linker[i])){
               linker[i]=u;
               return true;
           }
       }
    return false;
 }

 int main(){
    while(scanf("%d%d", &n, &m) && (n||m)){
        memset(g, , sizeof(g));
        while(m--){
           int u, v;
           scanf("%d%d", &u, &v);
           g[u][v]=;
        }
        for(int k=; k<=n; ++k)
           for(int i=; i<=n; ++i)
              for(int j=; j<=n; ++j)
                if(!g[i][j])
                   g[i][j]=g[i][k]&&g[k][j];
        memset(linker, , sizeof(linker));
        int ans=;
        for(int i=; i<=n; ++i){
            memset(vis, , sizeof(vis));
            if(dfs(i))  ++ans;
        }
        printf("%d\n", n-ans);
    }
    return ;
 }