Cod sursa(job #2492235)

Utilizator RaduPatraRadu Patra RaduPatra Data 14 noiembrie 2019 10:49:00
Problema Cele mai apropiate puncte din plan Scor 0
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.9 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;
};

int compareX(const void* a, const void* b)
{
	Point* p1 = (Point*)a, * p2 = (Point*)b;
	return (p1->x - p2->x);
}

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

float dist(Point p1, Point p2)
{
	return sqrt((p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y));
}

float bruteForce(Point P[], int n)
{
	float min = 999999999999;
	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 ClosestMid(Point midarr[], int size, float d)
{
	float min = d; 

	qsort(midarr, size, sizeof(Point), compareY);

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

	return min;
}

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

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

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

	float d = min(dl, dr);

	Point midarr[100];
	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));
}

float closest(Point P[], int n)
{
	qsort(P, n, sizeof(Point), 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;
	}

	out <<setprecision(10)<<closest(P, n);
	return 0;
}