hdu1565+hdu1569（最大点权独立集）

#pragma comment(linker,"/STACK:1024000000,1024000000")
#include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <limits.h>
#include <iostream>
#include <algorithm>
#include <queue>
#include <cstdlib>
#include <stack>
#include <vector>
#include <set>
#include <map>
#define LL long long
#define mod 100000000
#define inf 0x3f3f3f3f
#define eps 1e-6
#define N 2510
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define PII pair<int,int>
using namespace std;
inline int read()
{
    char ch=getchar();
    int x=0,f=1;
    while(ch>‘9‘||ch<‘0‘){if(ch==‘-‘)f=-1;ch=getchar();}
    while(ch<=‘9‘&&ch>=‘0‘){x=x*10+ch-‘0‘;ch=getchar();}
    return x*f;
}
int n,m,vs,vt,tot,NV;
int head[N],gap[N],level[N],q[N];
struct edge
{
    int v,w,next;
    edge(){}
    edge(int v,int w,int next):v(v),w(w),next(next){}
}e[N*N];
void addedge(int u,int v,int w)
{
    e[tot]=edge(v,w,head[u]);
    head[u]=tot++;
    e[tot]=edge(u,0,head[v]);
    head[v]=tot++;
}
void init()
{
    memset(head,-1,sizeof(head));
    tot=0;
}
/***************************SAP***********************/
void bfs(int vt)
{
    memset(level,-1,sizeof(level));
    memset(gap,0,sizeof(gap));
    level[vt]=0;
    gap[level[vt]]++;
    queue<int>que;
    que.push(vt);
    while(!que.empty()) {
        int u=que.front();
        que.pop();
        for(int i=head[u]; i!=-1; i=e[i].next) {
            int v=e[i].v;
            if(level[v]!=-1)continue;
            level[v]=level[u]+1;
            gap[level[v]]++;
            que.push(v);

        }
    }
}
int pre[N];
int cur[N];
int SAP()
{
    bfs(vt);
    memset(pre,-1,sizeof(pre));
    memcpy(cur,head,sizeof(head));
    int u=pre[vs]=vs,flow=0,aug=inf;
    gap[0]=NV;
    while(level[vs]<NV) {
        bool flag=false;
        for(int &i=cur[u]; i!=-1; i=e[i].next) {
            int v=e[i].v;
            if(e[i].w&&level[u]==level[v]+1) {
                flag=true;
                pre[v]=u;
                u=v;
                aug=min(aug,e[i].w);
                if(v==vt) {
                    flow+=aug;
                    for(u=pre[v]; v!=vs; v=u,u=pre[u]) {
                        e[cur[u]].w-=aug;
                        e[cur[u]^1].w+=aug;
                    }
                    aug=inf;
                }
                break;
            }
        }
        if(flag)continue;
        int minlevel=NV;
        for(int i=head[u]; i!=-1; i=e[i].next) {
            int v=e[i].v;
            if(e[i].w&&level[v]<minlevel) {
                minlevel=level[v];
                cur[u]=i;
            }
        }
        if(--gap[level[u]]==0)break;
        level[u]=minlevel+1;
        gap[level[u]]++;
        u=pre[u];
    }
    return flow;
}
/**************************SAP**********************/
int sum,x,num[55][55],id[55][55];
bool judge(int i,int j)
{
    return i>=1&&i<=n&&j>=1&&j<=m;
}
void build()
{
    sum=x=0;NV=n*m+2;
    vs=0;vt=n*m+1;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            x++;
            num[i][j]=read();
            sum+=num[i][j];
            id[i][j]=x;
        }
    }
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if((i+j)&1)
            {
                addedge(id[i][j],vt,num[i][j]);
            }
            else
            {
                addedge(vs,id[i][j],num[i][j]);
                for(int x=-1;x<=1;x++)
                for(int y=-1;y<=1;y++)
                {
                    if(x+y==0||x==y||!judge(x+i,y+j))continue;
                    addedge(id[i][j],id[i+x][j+y],inf);
                }
            }
        }
    }
}
int main()
{
    while(scanf("%d%d",&n,&m)>0)
    {
        init();
        build();
        printf("%d\n",sum-SAP());
    }
}