ZOJ2107——Quoit Design&&HDU1007——Quoit Design

#include<iostream>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
using namespace std;

struct point
{
    double x,y;
}p[100010];

int n;

bool cmp_x(point a,point b)
{
    return a.x<b.x;
}

bool cmp_y(point a,point b)
{
    return a.y<b.y;
}

double closest_pair(point *p,int n)
{
    if(n<=2)
    {
        return sqrt((p[1].x-p[0].x)*(p[1].x-p[0].x)+(p[1].y-p[0].y)*(p[1].y-p[0].y));
    }
    int m=n/2;
    double x=p[m].x;
    double d=min(closest_pair(p,m),closest_pair(p+m,n-m));
    inplace_merge(p,p+m,p+n,cmp_y);
    vector<point> b;
    for(int i=0;i<n;i++)
    {
        if(fabs(p[i].x-x)>=d)
            continue;
        for(int j=0;j<b.size();j++)
        {
            double dx=p[i].x-b[b.size()-j-1].x;
            double dy=p[i].y-b[b.size()-j-1].y;
            if(dy>=d)
                break;
            d=min(d,sqrt(dx*dx+dy*dy));
        }
        b.push_back(p[i]);
    }
    return d;
}

int main()
{
    while(scanf("%d",&n),n)
    {
        for(int i=0;i<n;i++)
            scanf("%lf%lf",&p[i].x,&p[i].y);
        sort(p,p+n,cmp_x);
        printf("%.2lf\n",closest_pair(p,n)/2);
    }
    return 0;
}