split_zip.rb

class Array
  def split_zip
    partition = size/2.0
    left  = first( partition.ceil )
    right = last(  partition.floor  )
    left.zip(right).flatten.compact
  end
end

          [1].split_zip == [1]           # => true
        [1,2].split_zip == [1,2]         # => true
      [1,2,3].split_zip == [1,3,2]       # => true
    [1,2,3,4].split_zip == [1,3,2,4]     # => true
  [1,2,3,4,5].split_zip == [1,4,2,5,3]   # => true
[1,2,3,4,5,6].split_zip == [1,4,2,5,3,6] # => true