bzoj 3232 圈地游戏 —— 01分数规划+最小割建图(最大权闭合子图)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#define eps 1e-6
#define inf 1e9
using namespace std;
int const xn=60,xm=3000,xe=5e4;//
int n,m,s,t,w[xn][xn],sid[xn][xn][xn][xn],S,T;
int dis[xm],hd[xm],ct=1,to[xe],nxt[xe],cur[xm];
int e1[xn][xn],e2[xn][xn];
double ans,c[xe],sum;
queue<int>q;
void add(int x,int y,double z)
{
    to[++ct]=y; nxt[ct]=hd[x]; c[ct]=z; hd[x]=ct;
    to[++ct]=x; nxt[ct]=hd[y]; c[ct]=0; hd[y]=ct;
}
int rd()
{
    int ret=0,f=1; char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=0; ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘)ret=(ret<<3)+(ret<<1)+ch-‘0‘,ch=getchar();
    return f?ret:-ret;
}
int id(int x,int y){return (x-1)*m+y;}
int P(int x,int y){return (x-1)*m+y;}

bool bfs()
{
    while(q.size())q.pop();
    memset(dis,0,sizeof dis);
    dis[s]=1; q.push(s);
    while(q.size())
    {
        int x=q.front(); q.pop();
        for(int i=hd[x],u;i;i=nxt[i])
            if(!dis[u=to[i]]&&c[i]>eps)dis[u]=dis[x]+1,q.push(u);
    }
    return dis[t];
}
double dfs(int x,double fl)
{
    if(x==t)return fl;
    double ret=0;
    for(int &i=cur[x],u;i;i=nxt[i])
    {
        if(dis[u=to[i]]!=dis[x]+1||c[i]<=eps)continue;
        double tmp=dfs(u,min(fl-ret,c[i]));
        if(tmp<eps)dis[u]=0;
        c[i]-=tmp; c[i^1]+=tmp;
        ret+=tmp; if(fl-ret<eps)return ret;
    }
    return ret;
}
bool ck(double k)
{
    memset(hd,0,sizeof hd); ct=1;//=1 而不是 0 !!!!!!!!!!!!!!!!!!!!!!!
    s=0; t=n*m+1;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
        {
            int x=id(i,j);
            add(s,x,w[i][j]);
            if(i==1)add(x,t,sid[i-1][j][i][j]*k);
            if(j==1)add(x,t,sid[i][j-1][i][j]*k);
            if(i==n)add(x,t,sid[i][j][i+1][j]*k);
            if(j==m)add(x,t,sid[i][j][i][j+1]*k);
            int y=id(i+1,j),z=id(i,j+1);
            if(i<n)add(x,y,k*sid[i][j][i+1][j]),add(y,x,k*sid[i][j][i+1][j]);
            if(j<m)add(x,z,k*sid[i][j][i][j+1]),add(z,x,k*sid[i][j][i][j+1]);//k*!!!
        }
    double ans=0;
    while(bfs())
    {
        memcpy(cur,hd,sizeof hd);
        ans+=dfs(0,inf);
    }
    return sum-ans>eps;
}
int main()
{
    n=rd(); m=rd(); s=0; t=n*m+1; double l=0,r=0;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)w[i][j]=rd(),r+=w[i][j],sum+=w[i][j];
    for(int i=1;i<=n+1;i++)
        for(int j=1;j<=m;j++)sid[i-1][j][i][j]=rd();
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m+1;j++)sid[i][j-1][i][j]=rd();
    while(l-r<=eps)
    {
        double mid=(l+r)*0.5;
        if(ck(mid))ans=mid,l=mid+eps;
        else r=mid-eps;
    }
    printf("%.3lf\n",ans);
    return 0;
}