marker.rb

module Codebreaker
  class Marker

    EXACT_MATCH_INDICATOR = 'b'
    COLOR_MATCH_INDICATOR = 'w'

    def self.mark(secret, guess)
      marker = self.new(secret)
      marker.guess(guess)
      marker.mark
    end

    def initialize(secret)
      @secret = secret
    end

    def guess(guess)
      @guess = guess
    end

    def exact_match_count
      [@guess, @secret].transpose.count {|a,b| a == b}
    end

    def color_match_count
      shared_frequencies.values.inject {|sum,count| sum+=count; sum}
    end

   def shared_frequencies
      (@secret & @guess).inject({}) do |frequencies,color|
        frequencies[color] = [
          @guess.count(color),
          @secret.count(color)
        ].min
        frequencies
      end
    end

    def mark
      [EXACT_MATCH_INDICATOR]*exact_match_count + [COLOR_MATCH_INDICATOR]*(color_match_count - exact_match_count)
    end

  end
end

marker_spec.rb

require 'spec_helper'

module Codebreaker
  describe Marker do
    context "class methods" do
      describe "#mark" do
        it "returns the mark for the submitted secret and guess" do
          Marker.mark(%w[r y g c], %w[r y g c]).should == %w[b b b b]
        end
      end
    end

    let(:marker) {Marker.new(%w[r g y c])}

    context "with all 4 colors correct in the correct places" do
      before(:each) do
        marker.guess %w[r g y c]
      end

      it "marks the guess with bbbb" do
        marker.mark.should == %w[b b b b]
      end

      it "returns 4 from #exact_match_count" do
        marker.exact_match_count.should == 4
      end

      it "returns 4 from #color_match_count" do
        marker.color_match_count.should == 4
      end
    end

    context "with all 4 colors correct, 2 in the correct places" do
      before(:each) do
        marker.guess %w[r g c y]
      end

      it "marks the guess with bbww" do
        marker.mark.should == %w[b b w w]
      end

      it "returns 2 from #exact_match_count" do
        marker.exact_match_count.should == 2
      end

      it "returns 4 from #color_match_count" do
        marker.color_match_count.should == 4
      end
    end

    context "with all 4 colors correct, 1 in the correct place" do
      before(:each) do
        marker.guess %w[y r g c]
      end

      it "marks the guess with bwww" do
        marker.mark.should == %w[b w w w]
      end

      it "returns 1 from #exact_match_count" do
        marker.exact_match_count.should == 1
      end

      it "returns 4 from #color_match_count" do
        marker.color_match_count.should == 4
      end
    end

    context "with three colors correct in the correct places" do
      before(:each) do
        marker.guess %w[r g y w]
      end

      it "marks the guess with bbb" do
        marker.mark.should == %w[b b b]
      end

      it "returns 3 from #exact_match_count" do
        marker.exact_match_count.should == 3
      end

      it "returns 3 from #color_match_count" do
        marker.color_match_count.should == 3
      end
    end

    context "with duplicates in the guess that match a peg in the code" do
      context "by color and position" do
        before(:each) do
          marker.guess %w[r g y y]
        end

        it "adds a single b to the mark for that color" do
          marker.mark.should == %w[b b b]
        end

        it "only accounts for the dup once in #exact_match_count" do
          marker.exact_match_count.should == 3
        end

        it "only accounts for the dup once in #color_match_count" do
          marker.color_match_count.should == 3
        end
      end

      context "by color only" do
        before(:each) do
          marker.guess %w[y y w y]
        end

        it "adds a single w to the mark for that color" do
          marker.mark.should == %w[w]
        end

        it "does not account for the dup at all in #exact_match_count" do
          marker.exact_match_count.should == 0
        end

        it "only accounts for the dup once in #color_match_count" do
          marker.color_match_count.should == 1
        end
      end
    end

    context "with duplications in the guess and code" do
      it "correctly accounts for the dups" do
        marker = Marker.new(%w[r r y g])
        marker.guess(%w[r r y g])
        marker.mark.should == %w[b b b b]
      end
    end
  end
end

output.txt

Codebreaker::Marker
  class methods
    #mark
      returns the mark for the submitted secret and guess
  with all 4 colors correct in the correct places
    marks the guess with bbbb
    returns 4 from #exact_match_count
    returns 4 from #color_match_count
  with all 4 colors correct, 2 in the correct places
    marks the guess with bbww
    returns 2 from #exact_match_count
    returns 4 from #color_match_count
  with all 4 colors correct, 1 in the correct place
    marks the guess with bwww
    returns 1 from #exact_match_count
    returns 4 from #color_match_count
  with three colors correct in the correct places
    marks the guess with bbb
    returns 3 from #exact_match_count
    returns 3 from #color_match_count
  with duplicates in the guess that match a peg in the code
    by color and position
      adds a single b to the mark for that color
      only accounts for the dup once in #exact_match_count
      only accounts for the dup once in #color_match_count
    by color only
      adds a single w to the mark for that color
      does not account for the dup at all in #exact_match_count
      only accounts for the dup once in #color_match_count
  with duplications in the guess and code
    correctly accounts for the dups