Match Ranking

ranking.rb

class Ranking
  def initialize(list)
    @list = list
  end

  def ranking
    @list.map { |c| c.last.zero? ? 0 : 1 + c.last }.reduce(&:+)
  end

  def sort(lists)
    lists.map { |t| [Ranking.new(t).ranking, t] }.sort.reverse.map(&:last)
  end
end

ranking_spec.rb

require_relative 'ranking.rb'

describe Ranking do
  subject { described_class }

  let(:trade)   { [[1, 4], [2, 2], [3, 2], [4, 4], [5, 1]] } # 18
  let(:trader1) { [[1, 2], [2, 0], [3, 4], [4, 4], [5, 0]] } # 13
  let(:trader2) { [[1, 4], [2, 1], [3, 0], [4, 3], [5, 4]] } # 16

  it { expect(subject.new(trade).ranking).to   eql 18 }
  it { expect(subject.new(trader1).ranking).to eql 13 }
  it { expect(subject.new(trader2).ranking).to eql 16 }

  it { expect(subject.new(trade).sort([trader1, trader2])).to eql([trader2, trader1]) }
end