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  • 【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;
    }
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  • 原文地址:https://www.cnblogs.com/cellular-automaton/p/8204872.html
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