Closest Pair

#include <bits/stdc++.h>

using namespace std;

struct point
{
    int x, y;
};

bool compare1 (const point &a, const point &b)
{
    return a.x>b.x;
}

bool compare2 (const point &a, const point &b)
{
    return a.y>b.y;
}

double dist(point a, point b)
{
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}

double dist2(point P[], int n)
{
    double minn=10000.0;
    for (int i=0; i<n; i++)
    {
        for (int j=i+1; j<n; j++)
        {
            if (dist(P[i], P[j]) < minn)
            {
                minn = dist(P[i], P[j]);
            }
        }
    }
    return minn;
}

double stripClosest (point strip[], int n, float d)
{
    float minn = d;
    for (int i=0; i<n; i++)
    {
        for (int j=i+1; j<n && (strip[j].y-strip[i].y)<minn; j++)
        {
            if (dist(strip[i],strip[j]) < minn)
            {
                minn=dist(strip[i], strip[j]);
            }
        }
    }

    return minn;
}

double closestUtil(point Px[], point Py[], int n)
{
    if (n <= 3) return dist2(Px, n);
    int mid = n/2;
    point midpoint = Px[mid];
    point PyL[mid+1];
    point PyR[n-mid-1];
    int l=0, r=0;
    for (int i=0; i<n; i++)
    {
        if (Py[i].x <= midpoint.x) PyL[l++] = Py[i];
        else PyR[r++] = Py[i];
    }
    double dl = closestUtil (Px, PyL, mid);
    double dr = closestUtil (Px + mid, PyR, n-mid);
    double 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 min(d, stripClosest(strip, j, d) );
}

double closest(point P[], int n)
{
    point Px[n], Py[n];
    for (int i=0; i<n; i++)
    {
        Px[i]=P[i];
        Py[i]=P[i];
    }
    sort (Px, Px+n, compare1);
    sort (Py, Py+n, compare2);

    return closestUtil(Px, Py, n);
}

int main()
{
    int n, x, y;
    scanf("%d", &n);
    point P[n];
    for (int i=0; i<n; i++)
    {
        scanf("%d%d", &P[i].x, &P[i].y);
    }
    double ans = closest(P, n);
    printf("\nDistance is: %lf\n", ans);
    return 0;
}