1011 最近点对

#include<iostream>
#include<cfloat>
#include<math.h>
#include<iomanip>
using namespace std;

struct Point
{
    int x;
    int y;
};


// http://www.cplusplus.com/reference/cstdlib/qsort/  qsort函数需要compar函数原型
int compareX(const void* a, const void* b)
{
    Point *p1 = (Point *)a, *p2 = (Point *)b;
    return (p1->x != p2->x) ? (p1->x - p2->x) : (p1->y - p2->y);
}

int compareY(const void* a, const void* b)
{
    Point *p1 = (Point *)a, *p2 = (Point *)b;
    return (p1->y != p2->y) ? (p1->y - p2->y) : (p1->x - p2->x);
}


float dist(Point p1, Point p2)
{
    // 乘以1.0防止int类型溢出
    float x = sqrt( 1.0*(p1.x - p2.x)*1.0*(p1.x - p2.x) + 1.0*(p1.y - p2.y)*1.0*(p1.y - p2.y));
    return x;
}

float bruteForce(Point P[], int n)
{
    float min = FLT_MAX;
    for (int i = 0; i < n; ++i)
        for (int j = i+1; j < n; ++j)
            if (dist(P[i], P[j]) < min)
                min = dist(P[i], P[j]);
    return min;
}

float min(float x, float y)
{
    return (x < y)? x : y;
}


float stripClosest(Point strip[], int size, float d)
{
    float min = d; 

    for (int i = 0; i < size; ++i)
        for (int j = i+1; j < size && (strip[j].y - strip[i].y) < min; ++j)
            if (dist(strip[i],strip[j]) < min)
                min = dist(strip[i], strip[j]);

    return min;
}

float closestUtil(Point Px[], Point Py[], int n)
{
    if (n <= 3)
        return bruteForce(Px, n);

    int mid = n/2;
    Point midPoint = Px[mid];


    Point Pyl[mid];
    Point Pyr[n-mid]; 
    int li = 0, ri = 0; 
    for (int i = 0; i < n; i++)
    {
    if ((Py[i].x < midPoint.x || (Py[i].x == midPoint.x && Py[i].y < midPoint.y)) && li<mid)
        Pyl[li++] = Py[i];
    else
        Pyr[ri++] = Py[i];
    }

    float dl = closestUtil(Px, Pyl, mid);
    float dr = closestUtil(Px + mid, Pyr, n-mid);

    float d = min(dl, dr);

    Point strip[n];
    int j = 0;
    for (int i = 0; i < n; i++)
        if (abs(Py[i].x - midPoint.x) < d)
            strip[j] = Py[i], j++;

    return stripClosest(strip, j, d);
}

float closest(Point P[], int n)
{
    Point Px[n];
    Point Py[n];
    for (int i = 0; i < n; i++)
    {
        Px[i] = P[i];
        Py[i] = P[i];
    }

    qsort(Px, n, sizeof(Point), compareX);
    qsort(Py, n, sizeof(Point), compareY);

    return closestUtil(Px, Py, n);
}




int main() {
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        int size;
        cin>>size;
        Point P[size];
        for(int i=0;i<size;i++)
        {
            Point p;
            cin>>p.x;
            cin>>p.y;
            P[i] = p;
        }

        cout<<fixed<<setprecision(2)<<closest(P, size) << endl;
    }
   return 0;
}