poj2007

极角排序，其实是叉乘排序

#include <iostream>
#include <algorithm>
#include <math.h>
#include <vector>

using namespace std;

#define eps 1e-8

struct point
{
	double x, y;
} s;

double getangle(point a)
{
	return atan2(a.y, a.x);
}
double xmult(point p1, point p2, point p0)
{
	return (p1.x - p0.x)*(p2.y - p0.y) - (p2.x - p0.x)*(p1.y - p0.y);
}
bool operator < (point a, point b)
{
	return xmult(a, b, s) > eps;
}

int main()
{
	vector<point> p;
	double a, b;
	//freopen("D:\b.txt", "r", stdin);
	cin >> s.x >> s.y;
	while (cin >> a >> b)
	{
		point temp;
		temp.x = a, temp.y = b;
		p.push_back(temp);
	}
	sort(p.begin(), p.end());
	cout << "(0,0)" << endl;
	for (vector<point>::iterator it = p.begin(); it != p.end(); ++it)
	{
		cout << '(' << (*it).x << ',' << (*it).y << ')' << endl;
	}
}