【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=0,f=1;
    char ch=getchar();
    while(!isdigit(ch)){
        if(ch=='-')    f=-1;
        ch=getchar();
    }
    while(isdigit(ch)){
        num=num*10+ch-'0';
        ch=getchar();
    }
    return num*f;
}
int n,m;
inline int count(int i){    return i&1?i+1:i-1;    }
inline int calc(int x,int y){    return (x-1)*m+y;    }

struct Edge{
    int next,to,val;
}edge[maxn*5];
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,0);
}

bool vis[maxn];
int dfn[maxn];
int list[maxn];
int Start=0,End;
int u[5]={0,0,1,0,-1};
int w[5]={0,1,0,-1,0};

bool bfs(){
    memset(vis,0,sizeof(vis));
    queue<int>q;    q.push(Start);    vis[Start]=1;    dfn[Start]=1;
    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==0||vis[to])    continue;
            vis[to]=1;    dfn[to]=dfn[from]+1;
            q.push(to);
        }
    }
    return vis[End];
}

int dfs(int x,int val){
    if(val==0||x==End)    return val;
    int flow=0;    vis[x]=1;
    for(int &i=list[x];i;i=edge[i].next){
        int to=edge[i].to;
        if(vis[to]||edge[i].val==0||dfn[to]!=dfn[x]+1)    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<=0)    break;
    }
    if(val!=flow)    dfn[x]=-1;
    return flow;
}

int maxflow(){
    int ans=0;
    while(bfs()){
        memset(vis,0,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+1;
    for(int i=1;i<=n;++i)
        for(int j=1;j<=m;++j){
            int x=read();sum+=x;
            if((i+j)&1){
                add(Start,calc(i,j),x);
                for(int k=1;k<=4;++k){
                    int a=i+u[k];    int b=j+w[k];
                    if(a==0||b==0||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 0;
}