HDOJ1007(平面上连点之间距离)

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
#define N 1000010
struct point 
{
 double x;
 double y;
}p1[N],pxSmall[N],pxLarge[N];
double dis ( point a , point b )
{
    return sqrt( pow (a.x-b.x,2) + pow ( a.y-b.y,2 ) );
}

double min ( double a , double b )
{
    return a<b?a:b;
}

bool cpx ( point a , point b )
{
    return a.x < b.x ;
}
bool cpy ( point a , point b )
{
    return a.y < b.y ;
}

double mindis (int l, int r)
{
    if( l + 1 == r )
        return dis ( p1[l] ,p1[r] );
    if( l + 2 == r )
        return min ( dis ( p1[l] , p1[l+1] ) , min ( dis ( p1[l+1] , p1[r] ) , dis ( p1[l] , p1[r] ) ) );
    else
    {
        int mid ,count1=0, count2=0;
        double mini;
        mid = ( l + r) >> 1 ;
        mini = min ( mindis ( l , mid ) , mindis ( mid+1 , r ) );
        for( int i = l ; i <= r ; i++ )
        {
            if ( fabs ( p1[i].x - p1[mid].x ) <= mini )
            {
                if (p1[i].x-p1[mid].x < 0)
                    pxSmall[count1++]=p1[i];
                else
                    pxLarge[count2++]=p1[i];
            }
                
        }
        //直接遍历两个数组
        for(int i=0;i<count1;i++)
        {
            for(int j=0;j<count2;j++)
            {
                double temp = dis(pxSmall[i], pxLarge[j]); 
                if(temp<mini)
                    mini=temp;
            }
        }
        
        return mini;
    }
}
int main()
{
    int n ;
    double dia ;
    while(scanf("%d",&n)==1&&n)
    {
        for(int i=0;i<n;i++)
        scanf("%lf%lf",&p1[i].x,&p1[i].y);
        sort ( p1 , p1 + n-1 , cpx );
        dia = mindis ( 0 , n-1 );
        printf("%.2f\n", dia / 2 );
    }
    return 0;
}