test.rb

require 'rspec'
require 'ap'

FILE = <<EOF
10.1.4.4 165.91.182.7
10.1.4.5 165.91.182.7
10.1.4.6 165.91.182.8
165.91.187.3 165.91.187.3
192.168.1.3
10.0.0.5 10.0.0.1
10.5.5.5
10.1.4.10 165.91.182.7
EOF

def calulate_structure
  stash = []
  group = {}
  order = []
  FILE.split("\n").each do |line|
    local, public = line.split("\s")
    key = public || local
    group[key] ||= []
    group[key].push [local, public]
    order.push(key) if !order.member? key
  end

  order.each do |key|
    if group[key].size == 1
      stash.push group[key].pop
    else
      stash.push group[key]
    end
  end
  stash
end

describe 'The Data Structure' do
  expected = [
              [
               ['10.1.4.4', '165.91.182.7'],
               ['10.1.4.5', '165.91.182.7'],
               ['10.1.4.10','165.91.182.7'],
              ],
              ['10.1.4.6', '165.91.182.8'],
              ['165.91.187.3', '165.91.187.3'],
              ['192.168.1.3', nil],
              ['10.0.0.5', '10.0.0.1'],
              ['10.5.5.5', nil],
             ]

  it 'should be the same' do
    calulate_structure.should == expected
  end
end