POJ 3041 Asteroids 匈牙利算法,最大流解法,行列为点 难度:1

http://poj.org/problem?id=3041

#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;
int e[1004][1004];
bool vis[1004];
vector <int > G[1004];
int n,m;
int dfs(int s){
    vis[s]=true;
    if(s==n*2+1){//printf("dfs ok %d\n",s);
    return 1;}
    for(int i=0;i<G[s].size();i++){
        int t=G[s][i];
        if(!vis[t]&&e[s][t]>0){
            if(dfs(t)>0){
                e[s][t]-=1;
                e[t][s]+=1;
                //printf("dfs ok %d\n",s);
                return 1;
            }
        }
    }
   // printf("dfs failed %d\n",s);
    return 0;
}
void printe(){
        for(int i=0;i<=2*n+1;i++){
            for(int j=0;j<=2*n+1;j++){
                if(e[i][j])printf("e[%d][%d]%d ",i,j,e[i][j]);
            }
            printf("\n");
        }
        printf("\n");
}
int maxflow(){
//printe();
    int ans=0,f;
    while(1){
        f=dfs(0);
//printe();
        memset(vis,0,sizeof(vis));
        if(f==0)return ans;
        ans+=f;
    }
}
int main(){
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++){e[0][i]=1;e[i][0]=0;G[0].push_back(i);}
    for(int i=n+1;i<=2*n;i++){e[i][2*n+1]=1;e[2*n+1][i]=0;G[i].push_back(2*n+1);}
    for(int i=0;i<m;i++){
        int f,t;
        scanf("%d%d",&f,&t);
        e[f][n+t]=1;
        e[n+t][f]=0;
        G[f].push_back(n+t);
        G[n+t].push_back(f);
    }
    int ans=maxflow();
    printf("%d\n",ans);
    return 0;
}