sequences.rb

require "minitest/autorun"
require "set"

class Sequencer
  def sequences(words)
    # go through all words
    #   go through each consecutive slice of 4
    #   look in the map for that slice
    #   add the word to the corresponding set
    # pick out the keys where values have 1 in the set
    h = Hash.new { Set.new } # new hash with set as default value
    pairs = words.reduce(h) do |seqs, word|
      word.chars.each_cons(4) do |sequence|
        seqs[sequence.join] += Set.new([word])
      end
      seqs
    end.select do |sequence, words|
      words.count == 1
    end.map do |sequence, words|
      [sequence, words.first]
    end.to_h
  end
end

class SequencesTest < Minitest::Test

  def input
    %w(arrows
       carrots
       give
       me)
  end

  def test_processing_list_of_words
    out = {"carr" => "carrots",
           "give" => "give",
           "rots" => "carrots",
           "rows" => "arrows",
           "rrot" => "carrots",
           "rrow" => "arrows"}
    assert_equal out, Sequencer.new.sequences(input)
  end
end