Suppose I have N points in two dimensional space.

I want to know which K of them are located most densely (so that area occupied by them will be least or sum of squares within cluster is least). Area occupied is area of polygon which connects least number points in the group so that all the points in the group are either inside the polygon or are on the boundary of polygon. How can I find them?

I know K-means-algorithm but it will yield groups that will have number of points different than K.