【bzoj1052】[HAOI2007]覆盖问题

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define Ll long long
using namespace std;
const Ll a[2][4]={{0,0,-1,-1},{0,-1,0,-1}};
const Ll INF=21474836470LL;
Ll sx[4],sy[4],ssx[4],ssy[4],x[20010],y[20010],up,dn,le,ri,n,maxlen,minlen;
bool boo[20010];
void cover(Ll xx,Ll yy,Ll len){
Ll U=xx,L=yy,D=xx+len-1,R=yy+len-1;
for (int i=1;i<=n;i++)
if (x[i]>=U&&x[i]<=D&&y[i]>=L&&y[i]<=R) boo[i]=1;
return;
}
bool in_square(Ll len){
Ll U=INF,D=-INF,R=-INF,L=INF;
for (int i=1;i<=n;i++)if (!boo[i]){
U=min(x[i],U);D=max(x[i],D);
R=max(y[i],R);L=min(y[i],L);
}
if ((D-U+1>len)||(R-L+1>len)) return 0;
return 1;
}
void getss(){
Ll U=INF,D=-INF,R=-INF,L=INF;
for (int i=1;i<=n;i++)if (!boo[i]){
U=min(x[i],U);D=max(x[i],D);
R=max(y[i],R);L=min(y[i],L);
}
ssx[0]=U;ssx[1]=U;ssx[2]=D;ssx[3]=D;
ssy[0]=L;ssy[1]=R;ssy[2]=L;ssy[3]=R;
return ;
}
bool ok(Ll len){
if ((len>=minlen)&&(len*3>=maxlen)) return 1;
for (int i=0;i<4;i++){
Ll x1=sx[i]+a[0][i]*(len-1);
Ll y1=sy[i]+a[1][i]*(len-1);
memset(boo,0,sizeof(boo));
cover(x1,y1,len);
if (in_square(len)) return 1;
getss();
for (int j=0;j<4;j++) {
memset(boo,0,sizeof(boo));
cover(x1,y1,len);
Ll x2=ssx[j]+a[0][j]*(len-1);
Ll y2=ssy[j]+a[1][j]*(len-1);
cover(x2,y2,len);
if (in_square(len)) return 1;
}
}
return 0;
}
int main(){
scanf("%d",&n);
up=INF;dn=-INF;
ri=-INF;le=INF;
for (int i=1;i<=n;i++){
scanf("%lld%lld",&x[i],&y[i]);
up=min(x[i],up);dn=max(x[i],dn);
ri=max(y[i],ri);le=min(y[i],le);
}
sx[0]=up;sx[1]=up;sx[2]=dn;sx[3]=dn;
sy[0]=le;sy[1]=ri;sy[2]=le;sy[3]=ri;
maxlen=max(dn-up+1,ri-le+1);
minlen=min(dn-up+1,ri-le+1);
Ll l=1LL,r=maxlen;
while (l!=r){
int mid=(l+r)>>1;
if (ok(mid)) r=mid;
else l=mid+1;
}
printf("%lld\n",l-1);
}