bzoj 3232: 圈地游戏

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
using namespace std;
const double eps=1e-5;
struct node{
int x,y,next,other;
double c;
}a[2110000];int last[3000],len=0;
int s[3000],h[3000],st,ed;
void ins(int x,int y,double c)
{
int k1=++len;
a[len].x=x;a[len].y=y;a[len].c=c;
a[len].next=last[x];last[x]=len;
int k2=++len;
a[len].x=y;a[len].y=x;a[len].c=0.0;
a[len].next=last[y];last[y]=len;
a[k1].other=k2;a[k2].other=k1;
}
bool bt_h()
{
memset(h,0,sizeof(h));
int l=1,r=2;s[l]=st;h[st]=1;
while(l!=r)
{
int x=s[l];
for(int i=last[x];i;i=a[i].next)
{
int y=a[i].y;
if(h[y]==0&&a[i].c>0) h[y]=h[x]+1,s[r++]=y;
}
l++;
}
return h[ed]!=0;
}
double findflow(int x,double f)
{
if(x==ed) return f;
double t,ans=0.0;
for(int i=last[x];i;i=a[i].next)
{
int y=a[i].y;
if(h[x]+1==h[y]&&a[i].c>0&&ans<f)
{
ans+=(t=findflow(y,min(a[i].c,f-ans)));
a[i].c-=t;a[a[i].other].c+=t;
}
}
if(ans==0) h[x]=0;
return ans;
}
int n,m,num=0;
int A[55][55],ys[55][55],he[55][55],sh[55][55];
bool check(double X)
{
memset(last,0,sizeof(last));len=0;
double tot=0;
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
{
int x=ys[i][j];
ins(st,x,(double)A[i][j]);
tot+=(double)A[i][j];
ins(x,ys[i-1][j],X*he[i][j]);
ins(x,ys[i+1][j],X*he[i+1][j]);
ins(x,ys[i][j-1],X*sh[i][j]);
ins(x,ys[i][j+1],X*sh[i][j+1]);
}
double ans=0.0;
while(bt_h()) ans+=findflow(st,999999999.0);
return tot-ans>0;
}
int main()
{
scanf("%d %d",&n,&m);
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++) scanf("%d",&A[i][j]);
for(int i=1;i<=n+1;i++)
for(int j=1;j<=m;j++) scanf("%d",&he[i][j]);
for(int i=1;i<=n;i++)
for(int j=1;j<=m+1;j++) scanf("%d",&sh[i][j]);
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++) ys[i][j]=++num;
st=0;ed=++num;
for(int i=1;i<=n;i++) ys[i][0]=ys[i][m+1]=ed;
for(int i=1;i<=m;i++) ys[0][i]=ys[n+1][i]=ed;
double l=0.0,r=2500000;
while(l+eps<r)
{
double mid=(l+r)/2;
if(check(mid)) l=mid;
else r=mid;
}
printf("%.3lf",l);
}