bzoj1052: [HAOI2007]覆盖问题（二分+构造）

#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdio> 
#include<algorithm>
#define ll long long 
using namespace std;
const int maxn=20010,inf=1e9;
typedef int poi[maxn];
poi x,y;
int n,m,l,r,mid,mxx,mxy,mnx,mny;
void read(int &k)
{
    int f=1;k=0;char c=getchar();
    while(c<‘0‘||c>‘9‘)c==‘-‘&&(f=-1),c=getchar();
    while(c<=‘9‘&&c>=‘0‘)k=k*10+c-‘0‘,c=getchar();
    k*=f;
}
void getmax(poi x,poi y,int tot,int &mxx,int &mxy,int &mnx,int &mny)
{
    mxx=mxy=-inf;mnx=mny=inf;
    for(int i=1;i<=tot;i++)
    {
        mxx=max(mxx,x[i]);mnx=min(mnx,x[i]);
        mxy=max(mxy,y[i]);mny=min(mny,y[i]);
    }
}
bool check(poi x,poi y,int tot,int dep)
{
    int mxx,mxy,mnx,mny,tot2;
    if(dep>2)
    {
        getmax(x,y,tot,mxx,mxy,mnx,mny);
        return max(mxx-mnx,mxy-mny)<=mid;
    }
    getmax(x,y,tot,mxx,mxy,mnx,mny);
    tot2=0;poi x2,y2;
    for(int i=1;i<=tot;i++)
    if(x[i]>mnx+mid||y[i]<mxy-mid)x2[++tot2]=x[i],y2[tot2]=y[i];
    if(check(x2,y2,tot2,dep+1))return 1;    
    tot2=0;
    for(int i=1;i<=tot;i++)
    if(x[i]<mxx-mid||y[i]<mxy-mid)x2[++tot2]=x[i],y2[tot2]=y[i];
    if(check(x2,y2,tot2,dep+1))return 1;
    tot2=0;
    for(int i=1;i<=tot;i++)
    if(x[i]>mnx+mid||y[i]>mny+mid)x2[++tot2]=x[i],y2[tot2]=y[i];
    if(check(x2,y2,tot2,dep+1))return 1;
    tot2=0;
    for(int i=1;i<=tot;i++)
    if(x[i]<mxx-mid||y[i]>mny+mid)x2[++tot2]=x[i],y2[tot2]=y[i];
    if(check(x2,y2,tot2,dep+1))return 1;
    return 0;
}
int main()
{
    read(n);
    for(int i=1;i<=n;i++)read(x[i]),read(y[i]);
    getmax(x,y,n,mxx,mxy,mnx,mny);
    l=1;r=max(mxx-mnx,mxy-mny);
    while(l<r)
    {
        mid=(l+r)>>1;
        if(check(x,y,n,1))r=mid;
        else l=mid+1;
    }
    printf("%d\n",l);
    return 0;
}