hint.rb

require 'minitest/autorun'

class ManhattanDistance
  # given a distance, calculate all possible move
  # possibilities a certain manhattan distance away
  def self.touples(n)
    return [] if n == 0

    list = []

    # build the list of all [x,y] pairs such that:
    # * x is an integer
    # * y is an integer
    # * x + y = n
  
    # list will then contain exactly all the elements EXACTLY n manhattan away
    # add in all of self.touples(n-1)
  end

  # convert a touple (x,y array pair) into 
  # versions for each 4 quadrants of the square
  def self.expand_touple(touple)
  	[
  		 #  x, y
  		 # -x, y
  		 #  x, -y
  		 # -x, -y
  	]
  end
end




class TestManhattanDistance < Minitest::Test
  require 'set' # set is nice because it will be equal even if order is mismatched

  def test_md
  	expected = [
  		[0,1], 
  		[1,0]
  	].to_set

  	assert_equal expected, ManhattanDistance.touples(1).to_set

 	expected = [
 		[0,1], [1,0],  # everything that is manhattan distance of 1 away
 		[1,1],         # up one, over one
 		[2, 0],        # over two
 		[0, 2]         # up two
 	].to_set

  	assert_equal expected, ManhattanDistance.touples(2).to_set

  end

  def test_expand_touple
  	touple = [1,1]
  	expected = [[1,1], [-1,1], [1,-1], [-1, -1]].to_set
  	assert_equal expected, ManhattanDistance.expand_touple(touple).to_set
  end
end