Sorting points by their polar angle in Java

Question

I\'m using Graham scan algorithm to find the convex-hull of set of points I\'m trying to sort the points by their polar angle but I have no idea how to do it (I\'ve already

Answer 1

As mentioned above, calculating the polar angle itself is a pretty sloppy way of going about things. You can define a simple comparator and use cross products to sort by polar angle. Here is code in C++ (which I use for my own Graham scan):

struct Point {
    int x, y;
}

int operator^(Point p1, Point p2) {
    return p1.x * p2.y - p1.y * p2.x;
}

bool operator<(Point p1, Point p2) 
{
    if(p1.y == 0 && p1.x > 0) 
        return true; //angle of p1 is 0, thus p2 > p1

    if(p2.y == 0 && p2.x > 0) 
        return false; //angle of p2 is 0 , thus p1 > p2

    if(p1.y > 0 && p2.y < 0) 
        return true; //p1 is between 0 and 180, p2 between 180 and 360

    if(p1.y <0 && p2.y > 0) 
         return false;

    return (p1 ^ p2) > 0; //return true if p1 is clockwise from p2
}

You can implement the same thing in Java, by defining a Point class. Basically I have overloaded the ^ operator to return the cross product. The rest is evident, hope this helps!