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;
}
}
