bzoj1052: [HAOI2007]覆盖问题（二分+搜索）

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<iostream>
#include<algorithm>
using namespace std;
struct node {int x,y;}a[21000];int n,b[21000],len=0;
const int inf=999999999;
bool check(int x) {
int up,down,right,left;up=-inf;right=-inf;down=inf;left=inf;
for(int i=1;i<=len;i++) {
up=max(up,a[b[i]].x);down=min(down,a[b[i]].x);
right=max(right,a[b[i]].y);left=min(left,a[b[i]].y);
}
bool bk=true;
for(int i=1;i<=len;i++) {
node t=a[b[i]];
if(!((t.x<=down+x&&t.y<=left+x)||(t.x>=up-x&&t.y>=right-x))) {bk=false;break;}
}if(bk==true)return true;bk=true;
for(int i=1;i<=len;i++) {
node t=a[b[i]];
if(!((t.x<=down+x&&t.y>=right-x)||(t.x>=up-x&&t.y<=left+x))) {bk=false;break;}
}if(bk==true)return true;return false;
}
void del(int up,int down,int left,int right) {
len=0;for(int i=1;i<=n;i++)if(a[i].x>up||a[i].x<down||a[i].y<left||a[i].y>right)b[++len]=i;
}
int main() {
scanf("%d",&n);int up,down,right,left;up=-inf;right=-inf;down=inf;left=inf;
for(int i=1;i<=n;i++) {
scanf("%d%d",&a[i].x,&a[i].y);
up=max(up,a[i].x);down=min(down,a[i].x);
right=max(right,a[i].y);left=min(left,a[i].y);
}
int l=1,r=max(up-down,right-left),mid,ans;
while(l<=r) {
mid=(l+r)/2;bool bk=false;
for(int i=1;i<=4;i++) {
if(i==1)del(up,up-mid,left,left+mid);
else if(i==2)del(up,up-mid,right-mid,right);
else if(i==3)del(down+mid,down,left,left+mid);
else del(down+mid,down,right-mid,right);
if(check(mid)==true) {bk=true;break;}
}if(bk==true) {ans=mid,r=mid-1;}else l=mid+1;
}printf("%d\n",ans);
return 0;
}