杭电 1007

//最短的两点距离#include <iostream>#include <cmath>#include <ctime>const double eps = 0.00001;struct Point{    double x;    double y;    int index;};const int N = 100000;//点的个数Point X[N];Point Y[N];Point C[N];double getDistance(Point a,Point b)//两点间的距离{    return sqrt(pow((a.x-b.x),2)+pow((a.y-b.y),2));}int cmp_x(const void *p, const void *q)//用于对X坐标进行排序{    double temp = ((Point*)p)->x - ((Point*)q)->x;    if (temp > 0)        return 1;    else if (fabs(temp) < eps)        return 0;    else        return  - 1;}int cmp_y(const void *p, const void *q)//用于对Y坐标进行排序{    double temp = ((Point*)p)->y - ((Point*)q)->y;    if (temp > 0)        return 1;    else if (fabs(temp) < eps)        return 0;    else        return  - 1;}double findCross(Point *Y,int l,int r, float x,float d){    int lcount = 0;    int rcount = 0;    double temp = 0;    int j=(r+l)/2+1;    for(int i=l;i<r;i++)//枚举所有可能，找出最小的    {        for (int j = i + 1; j <= r && Y[j].y - Y[i].y < d; j++)        {            double temp = getDistance(Y[i], Y [j]);            if (temp < d)                d = temp;        }    }    return d;}double divideConquer(Point X[],Point Y[],Point C[],int l,int r)//分治求最短距离{    if(l==r)//相等，返回无限大    {        return 100000;    }    else if(l+1==r)//相差一时返回两点的距离    {           return getDistance(X[l],X[r]);    }    else    {        int mid = (l+r)/2;        for(int i=l,j=l,k=mid+1;i<=r;i++)//按X的升序存入C中        {            if(Y[i].index<=mid)            {                C[j++] = Y[i];            }            else            {                C[k++] = Y[i];            }        }        double d1=divideConquer(X,C,Y,l,mid);        double d2=divideConquer(X,C,Y,mid+1,r);        double d = d1>d2?d2:d1;        d = findCross(C,l,r,X[mid].x,d);//求中间点的距离        return d;    }}int main(){    using std::cout;    using std::endl;    using std::cin;    int count=0;    while(cin>>count&&count>0)    {        double distance = -1;         for(int i=0;i<count;i++)         {            double x,y;            cin>>x;            cin>>y;            X[i].x = x;            X[i].y = y;            Y[i].x = x;            Y[i].y = y;                     }        qsort(X, count, sizeof(X[0]), cmp_x);//以x轴坐标排序        for(i=0;i<count;i++)        {            X[i].index = i;        }        memcpy(Y, X, count *sizeof(X[0]));//将X复制到Y中        qsort(Y, count, sizeof(Y[0]), cmp_y);//以y轴坐标排序        distance= divideConquer(X,Y,C,0,count-1);        printf("%.2lf\n",distance/2);     }    return 0;}