Mine

    private void addAllTransformations(int x){
        if(set.add(listToSkyline(list))&&x!=0){
            for(int i=0;i<list.size();i++){
                if(list.getBuilding(i).getLeft()-1>=leftBorder){
                    list.getBuilding(i).moveToLeft();
                    addAllTransformations(x-1);
                    list.getBuilding(i).moveToRight();
                }
                if(list.getBuilding(i).getRight()+1<=rightBorder){
                    list.getBuilding(i).moveToRight();
                    addAllTransformations(x-1);
                    list.getBuilding(i).moveToLeft();
                }
            }
        }
    }