分治 - 计算几何 - BZOJ2458,[BeiJing2011]最小三角形

考试时失了智，只拿了半个暴力分

其实这和平面最近点对方法一毛一样
除了多了一层循环
代码蒯上

#include<iostream>
#include<iomanip>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;
inline int gotcha()
{
	register int a=0;bool b=1;register char c=getchar();
	while(c>'9' || c<'0'){if(c=='-')b=0;c=getchar();}
	while(c>='0' && c<='9')a=a*10+c-48,c=getchar();
	return b?a:-a;
}
const double EPS = 1e-9;
const int _ = 200002;
using namespace std;
struct point{double x,y;}p[_];
inline bool init_cmp(const point &a,const point &b){return a.x<b.x;}
inline bool cmp(const int &a,const int &b){return p[a].y<p[b].y;}
inline double xdis(const int &a,const int &b){return fabs(p[a].x-p[b].x);}
inline double ydis(const int &a,const int &b){return fabs(p[a].y-p[b].y);}
double dist(int a,int b){return sqrt(xdis(a,b)*xdis(a,b)+ydis(a,b)*ydis(a,b));}
int n,q[_],lq;
double finder(int l,int r)
{	
	if(r<l+2)return 1e33;
	int i,j,k,mid=(l+r)>>1;
	double dis=min(finder(l,mid),finder(mid+1,r));
	lq=0;
	for(i=l;i<=r;i++)if(xdis(i,mid)<=dis/2)q[++lq]=i;
	sort(q+1,q+lq+1,cmp);
	for(i=1;i<=lq-2;i++)
		for(j=i+1;j<=lq-1 && ydis(q[i],q[j])<=dis/2;j++)
			for(k=j+1;k<=lq && ydis(q[i],q[k])<=dis/2;k++)
				dis=min(dis,dist(q[i],q[j])+dist(q[j],q[k])+dist(q[i],q[k]));
	return dis;
}
int main()
{
	register int i;
	n=gotcha();
	for(i=1;i<=n;i++)scanf("%lf%lf",&p[i].x,&p[i].y);
	sort(p+1,p+n+1,init_cmp);
	printf("%.6lf",finder(1,n));
	return 0;
}

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