Editing Graham scan (section)

== Pseudocode ==
The pseudocode below uses a function ccw: ccw > 0 if three points make a counter-clockwise turn, ccw < 0 if clockwise, and ccw = 0 if collinear. (In real applications, if the coordinates are arbitrary real numbers, the function requires exact comparison of floating-point numbers, and one has to beware of numeric singularities for "nearly" collinear points.)

Then let the result be stored in the <code>stack</code>.

 '''let''' points '''be''' the list of points
 '''let''' stack = empty_stack()
 
 '''find''' the lowest y-coordinate and leftmost point, called P0
 '''sort''' points by polar angle with P0, if several points have the same polar angle then only keep the farthest
 
 '''for''' point '''in''' points:
     # pop the last point from the stack if we turn clockwise to reach this point
     '''while''' '''count''' stack > 1 and '''ccw'''(next_to_top(stack), top(stack), point) <= 0:
         '''pop''' stack
     '''push''' point '''to''' stack
 '''end'''

Now the stack contains the convex hull, where the points are oriented counter-clockwise and P0 is the first point.

Here, <code>next_to_top()</code> is a function for returning the item one entry below the top of stack, without changing the stack, and similarly, <code>top()</code> for returning the topmost element.

This pseudocode is adapted from ''[[Introduction to Algorithms]]''.