angelikatyborska's solution to Queen Attack on the Ruby track

Instructions

Test suite

Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Given the position of two queens on a chess board, indicate whether or not they are positioned so that they can attack each other.

In the game of chess, a queen can attack pieces which are on the same row, column, or diagonal.

A chessboard can be represented by an 8 by 8 array.

So if you're told the white queen is at (2, 3) and the black queen at (5, 6), then you'd know you've got a set-up like so:

_ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _
_ _ _ W _ _ _ _
_ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _
_ _ _ _ _ _ B _
_ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _

You'd also be able to answer whether the queens can attack each other. In this case, that answer would be yes, they can, because both pieces share a diagonal.

For installation and learning resources, refer to the exercism help page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby queen_attack_test.rb

To include color from the command line:

ruby -r minitest/pride queen_attack_test.rb

Source

J Dalbey's Programming Practice problems http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

queen_attack_test.rb

require 'minitest/autorun'
require_relative 'queen_attack'

# Common test data version: 2.0.0 44a1e12
class QueenAttackTest < Minitest::Test
  def test_queen_with_a_valid_position
    # skip
    assert Queens.new(white: [2, 2])
  end

  def test_queen_must_have_positive_row
    skip
    assert_raises ArgumentError do
      Queens.new(white: [-2, 2])
    end
  end

  def test_queen_must_have_row_on_board
    skip
    assert_raises ArgumentError do
      Queens.new(white: [8, 4])
    end
  end

  def test_queen_must_have_positive_column
    skip
    assert_raises ArgumentError do
      Queens.new(white: [2, -2])
    end
  end

  def test_queen_must_have_column_on_board
    skip
    assert_raises ArgumentError do
      Queens.new(white: [4, 8])
    end
  end

  def test_can_not_attack
    skip
    queens = Queens.new(white: [2, 4], black: [6, 6])
    refute queens.attack?
  end

  def test_can_attack_on_same_row
    skip
    queens = Queens.new(white: [2, 4], black: [2, 6])
    assert queens.attack?
  end

  def test_can_attack_on_same_column
    skip
    queens = Queens.new(white: [4, 5], black: [2, 5])
    assert queens.attack?
  end

  def test_can_attack_on_first_diagonal
    skip
    queens = Queens.new(white: [2, 2], black: [0, 4])
    assert queens.attack?
  end

  def test_can_attack_on_second_diagonal
    skip
    queens = Queens.new(white: [2, 2], black: [3, 1])
    assert queens.attack?
  end

  def test_can_attack_on_third_diagonal
    skip
    queens = Queens.new(white: [2, 2], black: [1, 1])
    assert queens.attack?
  end

  def test_can_attack_on_fourth_diagonal
    skip
    queens = Queens.new(white: [2, 2], black: [5, 5])
    assert queens.attack?
  end

  # Problems in exercism evolve over time, as we find better ways to ask
  # questions.
  # The version number refers to the version of the problem you solved,
  # not your solution.
  #
  # Define a constant named VERSION inside of the top level BookKeeping
  # module, which may be placed near the end of your file.
  #
  # In your file, it will look like this:
  #
  # module BookKeeping
  #   VERSION = 1 # Where the version number matches the one in the test.
  # end
  #
  # If you are curious, read more about constants on RubyDoc:
  # http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html

  def test_bookkeeping
    skip
    assert_equal 2, BookKeeping::VERSION
  end
end

class Queens
  def initialize(white: nil, black: nil)
    @white = WhiteQueen.new
    @black = BlackQueen.new
    @chessboard = Chessboard.new({@white => white, @black => black})
  end

  def to_s
    @chessboard.to_s
  end

  def white
    @chessboard.pieces[@white]
  end

  def black
    @chessboard.pieces[@black]
  end

  def attack?
    @chessboard.attack?(@white, @chessboard.pieces[@black])
  end
end

class Queen
  def starting_position
    [0, 0]
  end

  def symbol
    'Q'
  end

  def attack?(chessboard, my_position, other_position)
    conditions = %w(same_column? same_row? diagonal?)
    conditions.any? { |condition| chessboard.send(condition, my_position, other_position) }
  end
end

class WhiteQueen < Queen
  def starting_position
    [0, 3]
  end

  def symbol
    'W'
  end
end

class BlackQueen < Queen
  def starting_position
    [7, 3]
  end

  def symbol
    'B'
  end
end

class Chessboard
  BOARD_SIZE = 8

  attr_reader :pieces

  def initialize(pieces = {})
    @pieces = {}

    pieces.each do |piece, piece_position|
      if @pieces.values.include?(piece_position)
        fail ArgumentError, "Position #{piece_position} already taken"
      end
      @pieces[piece] = piece_position || piece.starting_position
    end
  end

  def to_s
    board = Array.new(BOARD_SIZE) { Array.new(BOARD_SIZE) { '_' } }

    @pieces.each do |piece, piece_position|
      board[piece_position[0]][piece_position[1]] = piece.symbol
    end

    board.map { |row| row.join(' ') }.join("\n")
  end

  def attack?(piece, position)
    piece.attack?(self, @pieces[piece], position)
  end

  def same_column?(position1, position2)
    position1[0] == position2[0]
  end

  def same_row?(position1, position2)
    position1[1] == position2[1]
  end

  def diagonal?(position1, position2)
    (position1[0] - position2[0]).abs == (position1[1] - position2[1]).abs
  end
end

Community comments

Find this solution interesting? Ask the author a question to learn more.

kkelleey

commented almost 5 years ago

At first I liked how you made BOARD_SIZE a constant, but now that I think about it more, I might consider having it be a parameter at initialization in the Chessboard Class so that Chessboard can be used to generate a board of any size. It's really the Queens class that requires a board of size 8, so you could set it as a constant there.

Also, I like how you use Array.new to create the empty board. Did you know you can use the array index as a parameter in the block? (I didn't until I did this exercise). So instead of creating the array and then iterating over it again, you could set the piece symbol as you create it

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

What compromises have been made?
Are there new concepts here that you could read more about to improve your understanding?

angelikatyborska's solution

to Queen Attack in the Ruby Track