Ray casting algorithm is a method to determine whether a point lies inside a simple polygon or not. The method is to cast a ray from the point in some direction and count the number of sides of the polygon that intersect with the ray; if the count is odd, then it's inside, otherwise it's outside.

Assuming this means the problem is "determine whether a point lies in a polygon or not", the "winding number algorithm" is probably to compute the winding number of the polygon around the point; if it's 0, then the point is outside, otherwise it's inside.

The question is thus "how to implement this winding number algorithm".