[TYVJ1338] QQ农场

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int INF=1999999999;
int h[1000000],next[1000000],cap[1000000],to[1000000],k=1;
int level[40100],que[40100],head,tail,iter[40100],n;
int x[4]={-1,0,1,0},y[4]={0,-1,0,1}; 
void ins(int u,int v,int c){next[++k]=h[u];h[u]=k;to[k]=v;cap[k]=c;}
int get(int i,int j){return (i-1)*n+j;}
bool bfs(int S,int T)
{
    memset(level,0,sizeof(level));
    head=tail=0;que[tail++]=S;level[S]=1;
    while(head<tail)
    {
        int u=que[head++];
        for(int i=h[u];i;i=next[i])
        {
            int v=to[i];
            if(!level[v]&&cap[i])
            {
                level[v]=level[u]+1;que[tail++]=v;
            }
        }
    }
    if(!level[T])return 0;return 1;
}
int dfs(int u,int T,int f)
{
    if(u==T)return f;
    int used=0;
    for(int &i=iter[u];i;i=next[i])
    {
        int v=to[i];
        if(level[v]==level[u]+1&&cap[i])
        {
            int w=dfs(v,T,min(cap[i],f-used));used+=w;
            if(w)
            {
                cap[i]-=w;cap[i^1]+=w;if(f==used)return f;
            }
        }
    }
    return used;
}
int dinic(int S,int T)
{
    int flow=0;
    while(1)
    {
        for(int i=0;i<=n*n+1;i++)iter[i]=h[i];
        if(!bfs(S,T))return flow;flow+=dfs(S,T,INF);
    }
}
int main()
{
    scanf("%d",&n);int S=0,T=n*n+1,tot=0;
    for(int i=1;i<=n;i++)
    for(int j=1;j<=n;j++)
    {
        int v;scanf("%d",&v);tot+=v;
        if(i%2==j%2){ins(get(i,j),T,v);ins(T,get(i,j),0);}
        else 
        {
            for(int k=0;k<4;k++)
            {
                int ii=i+x[k],jj=j+y[k];if(ii<1||ii>n||jj<1||jj>n)continue;
                ins(get(i,j),get(ii,jj),INF);ins(get(ii,jj),get(i,j),0);
            }
            ins(S,get(i,j),v);ins(get(i,j),S,0);
        }
    }
    cout<<tot-dinic(S,T);
    return 0;
 }