【Luogu】P2774方格取数问题（最大点权独立集）

　　题目链接

　　不知道为啥坠大点权独立集的做法跟最大权闭合图差不多？

　　qwq

　　放个链接

#include<cstdio>
#include<cstring>
#include<cctype>
#include<algorithm>
#include<cstdlib>
#include<queue>
#define maxn 30000
using namespace std;
inline long long read(){
    long long num=,f=;
    char ch=getchar();
    while(!isdigit(ch)){
        if(ch=='-')    f=-;
        ch=getchar();
    }
    while(isdigit(ch)){
        num=num*+ch-'';
        ch=getchar();
    }
    return num*f;
}
int n,m;
inline int count(int i){    return i&?i+:i-;    }
inline int calc(int x,int y){    return (x-)*m+y;    }

struct Edge{
    int next,to,val;
}edge[maxn*];
int head[maxn],num;
inline void addedge(int from,int to,int val){
    edge[++num]=(Edge){head[from],to,val};
    head[from]=num;
}
inline void add(int from,int to,int val){
    addedge(from,to,val);
    addedge(to,from,);
}

bool vis[maxn];
int dfn[maxn];
int list[maxn];
int Start=,End;
int u[]={,,,,-};
int w[]={,,,-,};

bool bfs(){
    memset(vis,,sizeof(vis));
    queue<int>q;    q.push(Start);    vis[Start]=;    dfn[Start]=;
    while(!q.empty()){
        int from=q.front();    q.pop();
        for(int i=head[from];i;i=edge[i].next){
            int to=edge[i].to;
            if(edge[i].val==||vis[to])    continue;
            vis[to]=;    dfn[to]=dfn[from]+;
            q.push(to);
        }
    }
    return vis[End];
}

int dfs(int x,int val){
    if(val==||x==End)    return val;
    int flow=;    vis[x]=;
    for(int &i=list[x];i;i=edge[i].next){
        int to=edge[i].to;
        if(vis[to]||edge[i].val==||dfn[to]!=dfn[x]+)    continue;
        int now=dfs(to,min(val,edge[i].val));
        edge[i].val-=now;    edge[count(i)].val+=now;    val-=now;flow+=now;
        if(val<=)    break;
    }
    if(val!=flow)    dfn[x]=-;
    return flow;
}

int maxflow(){
    int ans=;
    while(bfs()){
        memset(vis,,sizeof(vis));
        for(int i=Start;i<=End;++i)    list[i]=head[i];
        int now=dfs(Start,0x7fffffff);
        if(!now)    break;
        ans+=now;
    }
    return ans;
}

int sum;

int main(){
    n=read(),m=read();    End=n*m+;
    for(int i=;i<=n;++i)
        for(int j=;j<=m;++j){
            int x=read();sum+=x;
            if((i+j)&){
                add(Start,calc(i,j),x);
                for(int k=;k<=;++k){
                    int a=i+u[k];    int b=j+w[k];
                    if(a==||b==||a>n||b>m)    continue;
                    add(calc(i,j),calc(a,b),0x7fffffff);
                }
            }
            else        add(calc(i,j),End,x);
        }
    int ans=maxflow();
    printf("%d",sum-ans);
    return ;
}