hdu2686/hdu3376 最小费用流最大流 拆点

  1 #include<iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<queue>
  5 #include<algorithm>
  6 using namespace std;
  7 const int N =1000010, M=4000100,INF=0x3f3f3f3f;
  8 struct node
  9 {
 10     int to, next, c ,f;//c是容量，f是费用
 11 }edge[M];
 12 int head[N],dis[N],load[N],p[N];
 13 bool vis[N];
 14 int tot,flow,cost;
 15 bool spfa(int S, int E,int n)
 16 {
 17     queue<int > que;
 18     memset(vis,0,sizeof(vis));
 19     memset(load,-1,sizeof(load));
 20     memset(p,-1,sizeof(p));
 21     for(int i=0;i<=n;i++)
 22         dis[i]=INF;
 23     que.push(S);
 24     dis[S]=0;
 25     vis[S]=1;
 26     while(!que.empty())
 27     {
 28         int u=que.front();
 29         que.pop();
 30         vis[u]=0;
 31         for(int i=head[u];i!=-1;i=edge[i].next)
 32         {
 33             if(edge[i].c)
 34             {
 35                 int v=edge[i].to;
 36                 if(dis[v]-dis[u]>edge[i].f)
 37                 {
 38                     dis[v]=dis[u]+edge[i].f;
 39                     p[v]=u;
 40                     load[v]=i;
 41                     if(!vis[v])
 42                     {
 43                         vis[v]=1;
 44                         que.push(v);
 45                     }
 46                 }
 47             }
 48         }
 49     }
 50     if(dis[E]==INF) return 0;
 51     return 1;
 52 }
 53 void MCF(int S, int E,int n)
 54 {
 55     int u,mn;
 56     flow=cost=0;
 57     while(spfa(S,E,n))
 58     {
 59         u=E; mn=INF;
 60         while(p[u]!=-1)
 61         {
 62             mn=min(edge[load[u]].c, mn);
 63             u=p[u];
 64         }
 65         u=E;
 66         while(p[u]!=-1)
 67         {
 68             edge[load[u]].c-=mn;
 69             edge[load[u]^1].c+=mn;
 70             u=p[u];
 71         }
 72         cost+=dis[E]*mn;
 73         flow+=mn;
 74     }
 75 }
 76 void addedge(int a,int b,int c,int d)
 77 {
 78     edge[tot].to=b;edge[tot].c=c;edge[tot].f=d;
 79     edge[tot].next=head[a];head[a]=tot++;
 80     edge[tot].to=a;edge[tot].c=0;edge[tot].f=-d;
 81     edge[tot].next=head[b];head[b]=tot++;
 82 }
 83 void init()
 84 {
 85     tot=0;
 86     memset(head,-1,sizeof(head));
 87 }
 88 int nd[N];
 89 int main()
 90 {
 91     //freopen("test.txt","r",stdin);
 92     int n,i,j,k,a,s,e,b;
 93     while(scanf("%d",&n)!=EOF)
 94     {
 95         init();
 96         b=n*n;
 97         s=2*b+1;e=s+1; a=100;
 98         for(i=1;i<=b;i++) {scanf("%d",&nd[i]);a=max(a,nd[i]);}
 99         a++;
100         addedge(s,1,2,0);
101         addedge(2*b,e,2,0);
102         for(i=1;i<=b;i++)
103         {
104             if(i==1) addedge(i,i+b,2,a-nd[i]);
105             else if(i==b) addedge(i,i+b,2,a-nd[i]);
106             else addedge(i,i+b,1,a-nd[i]);
107             if(i%n) addedge(i+b,i+1,1,0);//向右
108             if(i<=b-n) addedge(i+b,i+n,1,0);//向下
109         }
110         MCF(s,e,e);
111         cost-=a-nd[1]+a-nd[b];
112         int ans=4*a*(n-1)-cost;
113         printf("%d\n",ans);
114     }
115     return 0;
116 }