平面分治（求最近点对）

#include<cstdio>
#include<algorithm>
#include<cmath>
#define MAXN 10100 
#define INF 0x3f3f3f3f
using namespace std;
struct node{
	int x;
	int y;
}point[MAXN];
bool cmpx(node a,node b){
	return a.x < b.x;
}
bool cmpy(node c,node d){
	return c.y < d.y;
}
double min(double w,double v){
	return w <= v ? w : v;
}
double dis(node g,node p){
	return sqrt( (g.x-p.x)*(g.x-p.x) + (g.y-p.y)*(g.y-p.y) );
}
double point_b(int left,int right){
	double d=10000;
	if(left == right)	return d;
	if(left+1 == right)
		return dis(point[left], point[right]);
	double d1 , d2 ;
	int l = ( left + right ) / 2;
	d1 = point_b(left, l );
	d2 = point_b(l+1, right );
	d = min(d1, d2 );
	int i=left , j=right;
	while(i < l && point[l].x - point[i].x >= d)	i++;
	while(j > l && point[j].x - point[l].x >= d)	j--;
	sort(point + i + 1, point + j + 1, cmpy);
	for(int k=i ; k<=j ; k++)
	{
		for(int m=k+1 ; m<=j && point[m].y - point[k].y < d ; m++)
		{
			double d3=dis(point[m], point[k]);
			if(d > d3)
				d=d3;
		}
	}
	return d;
}
int main()
{
	int n;
	while(~scanf("%d",&n) && n)
	{
		for(int i=0 ; i<n ; i++)  
			scanf("%d %d",&point[i].x,&point[i].y);
		sort(point,point+n,cmpx);
		double temp=point_b(0,n-1);
		if(temp >= 10000)
			printf("INFINITY");
		else
			printf("%.4lf\n",temp);
	}
	return 0;
}