Cod sursa(job #2492263)

Utilizator RaduPatraRadu Patra RaduPatra Data 14 noiembrie 2019 11:35:39
Problema Cele mai apropiate puncte din plan Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.85 kb
// A divide and conquer program in C++  
// to find the smallest distance from a  
// given set of points.  

#include <iostream>
#include <fstream>
#include <algorithm>
#include <cmath>
#include <iomanip>
using namespace std;
ifstream in("cmap.in");
ofstream out("cmap.out");

struct Point
{
	int x, y;
};

bool compareX(Point p1, Point p2)
{
	return (p1.x < p2.x);
}


bool compareY(Point p1, Point p2)
{
	return (p1.y < p2.y);
}

double dist(Point p1, Point p2)
{

	double dist = sqrt(pow((p1.x - p2.x), 2) + pow((p1.y - p2.y), 2));
	return dist;
}

double bruteForce(Point P[], int n)
{
	double mini = 9999999999.0;
	for (int i = 0; i < n; ++i)
		for (int j = i + 1; j < n; ++j)
			if (dist(P[i], P[j]) < mini)
				mini = dist(P[i], P[j]);
	return mini;
}


double ClosestMid(Point midarr[], int size, double d)
{
	double mini = d; 

	sort(midarr, midarr + size, compareY);

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

	return mini;
}

double closestUtil(Point P[], int n)
{
	if (n <= 3)
		return bruteForce(P, n);

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

	double dl = closestUtil(P, mid);
	double dr = closestUtil(P + mid, n - mid);

	double d = min(dl, dr);

	Point* midarr = new Point[n];
	int j = 0;
	for (int i = 0; i < n; i++)
		if (abs(P[i].x - midPoint.x) < d)
		{
			midarr[j] = P[i];
			j++;
		}


	return min(d, ClosestMid(midarr, j, d));
}

double closest(Point P[], int n)
{
	sort(P, P + n, compareX);
	return closestUtil(P, n);
}

int main()
{
	int n,i;
	
	in >> n;
	Point * P = new Point[n];
	for (i = 0;i < n;i++)
	{
		in >> P[i].x >> P[i].y;
	}
	double r = closest(P, n);
	out <<fixed<<setprecision(6)<<r;
	return 0;
}