gistfile1.rb

# [] #=> []
# [:a] #=> []
# [:a, :b] #=> [:a] or [:b]
# [:a, :b, :c] #=> [:a, :b] or [:b, :c] or [:a, :c] 
# [:a, :b, :c, :d] #=> [:b, :c] or [:a, :c] or [:b, :d] or [:c, :d] 

def recommend_siblings_for(item, list)
  case list.size
  when 0,1
    []
  else
    i = list.at(item)
    case i
    when nil
      []
    when 0                      # head
      list[1..2]
    when list.length - 1        # tail
      # TODO
    else                        # interior
      [list[i-1], list[i+1]]
    end
  end
end