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  • 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
    ",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
    ",s);
                    return 1;
                }
            }
        }
       // printf("dfs failed %d
    ",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("
    ");
            }
            printf("
    ");
    }
    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
    ",ans);
        return 0;
    }
    

      

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  • 原文地址:https://www.cnblogs.com/xuesu/p/4755025.html
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