minesweeper.rb

class Cell
  attr_accessor :is_mine, :num_adjacent_mines
  def initialize
    self.num_adjacent_mines = 0
  end

  def to_s
    if is_mine
      '*'
    else
      num_adjacent_mines.zero? ? '.' : num_adjacent_mines.to_s
    end
  end
end

class Board
  def initialize(size = 10, num_mines = 20)
    @size = size
    @num_mines = num_mines
    clear
  end

  def clear
    @cells = Array.new(@size) { Array.new(@size) { Cell.new } }
  end

  def populate
    # populate mines
    empty_cells = @cells.flatten
    @num_mines.times do
      mined_cell = empty_cells[rand(empty_cells.size)].tap { |cell| cell.is_mine = true }
      empty_cells.delete mined_cell
    end
    # populate number of adjacent mines
    @cells.each_with_index do |row, i|
      row.each_with_index do |cell, j|
        cell.num_adjacent_mines = num_adjacent_mines_to(i, j) unless cell.is_mine
      end
    end
  end

  def to_s
    @cells.map(&:join).join("\n")
  end

  private
  def num_adjacent_mines_to(x, y)
    # don't go look past the borders of the board
    range = lambda { |i| ([i - 1, 0].max..[i + 1, @size - 1].min) }
    @cells[range.call(x)].inject(0) do |sum, row|
      sum += row[range.call(y)].select(&:is_mine).size
    end
  end
end

def setup
  @b = Board.new
  @b.populate
  puts @b
end