Kata

Sandy has to walk to the store. But for some reason she is given (x,y) coordinates of the candy store. Now she really loves coordinates, but she also loves options. If Sandy starts at position (0,0), how many ways can she walk to position (x,y) assuming that x,y > 0 and she can only walk to the right and up one unit.

Example:

The store is at (1,1). Sandy can walk Up, Right. Or Sandy can walk Right, Up. Sandy can walk two ways. --> options(1,1) --> 2.

Return null if x,y < 0