http://codingdojo.org/kata/Minesweeper/

minesweeper.rb

require "minitest/autorun"

class TestMine < Minitest::Test
  def test_1
    field = '*'
    expected_result = '*'

    assert_equal expected_result, minesweeper(1, 1, field)
  end

  def test_2
    field = '.*.'
    expected_result = '1*1'

    assert_equal expected_result, minesweeper(1, 3, field)
  end

  def test_3
    field = "...\n.*."
    expected_result = "111\n1*1"

    assert_equal expected_result, minesweeper(2, 3, field)
  end

  def test_4
    field = "...\n...\n..*"
    expected_result = "000\n011\n01*"

    assert_equal expected_result, minesweeper(3, 3, field)
  end

  def test_5
    field = "*..\n..*"
    expected_result = "*21\n12*"

    assert_equal expected_result, minesweeper(2, 3, field)
  end

  def test_6
    field = "*..\n..*\n..."
    expected_result = "*21\n12*\n011"

    assert_equal expected_result, minesweeper(3, 3, field)
  end

  def test_7
    field = "*..\n*.."
    expected_result = "*20\n*20"

    assert_equal expected_result, minesweeper(2, 3, field)
  end
end

MINE = '*'
NO_MINE = '.'
MINE_HINT = '*'
HINT = '1'
NO_HINT = '0'
ROW_SEPARATOR = "\n"

def minesweeper(rows, cols, field)
  hint_maps = each_mine(field) do |mine_pos|
    create_hint_map(field, mine_pos, rows, cols)
  end

  merge_maps(hint_maps)
end

def each_mine(field, &block)
  mine_pos = -1
  mines_count = 1..field.count(MINE)

  mines_count.map do
    mine_pos = field.index(MINE, mine_pos + 1)
    yield(mine_pos)
  end
end

def create_hint_map(field, mine_pos, rows, cols)
  hint_map = create_empty_hint_map_with_border(field, cols)
  mine_pos_with_border = add_border_offset(mine_pos, cols)

  add_hints(hint_map, mine_pos_with_border, cols)

  remove_border(hint_map, rows, cols)
end

def merge_maps(maps)
  maps.reduce do |merged, map|
    merge(merged, map)
  end
end

def remove_border(hint_map, rows, cols)
  border_per_row = 2
  hint_map_without_upper_border = hint_map[cols+border_per_row .. -1]

  (0..rows-1).map { |row|
    start = row * cols + row * border_per_row + 1
    hint_map_without_upper_border[start, cols]
  }.join(ROW_SEPARATOR)
end

def create_empty_hint_map_with_border(field, cols)
  empty_row = NO_HINT * (cols + 2)
  left_right_border = /$|^/

  hint_map = field.gsub(left_right_border, NO_HINT)
  hint_map = hint_map.tr(NO_MINE, NO_HINT)
  hint_map = hint_map.tr(ROW_SEPARATOR, '')
  empty_row + hint_map + empty_row
end

def add_hints(hint_map, pos, cols)
  add_hint(hint_map, pos - cols - 1)
  add_hint(hint_map, pos - cols - 2)
  add_hint(hint_map, pos - cols - 3)
  add_hint(hint_map, pos + cols + 1)
  add_hint(hint_map, pos + cols + 2)
  add_hint(hint_map, pos + cols + 3)
  add_hint(hint_map, pos - 1)
  add_hint(hint_map, pos + 1)
end

def merge(a_field, another_field)
  [a_field.chars, another_field.chars].transpose.map do |cell|
    cell.reduce do |sum, value|
      begin
        (Integer(value) + Integer(sum)).to_s
      rescue
        value
      end
    end
  end.join
end

def add_border_offset(pos, cols)
  separator_per_line = ROW_SEPARATOR.length
  upper_border = cols + 2
  cols_with_separator = cols + separator_per_line

  offset = upper_border + separator_per_line + (pos / cols_with_separator)

  pos + offset
end

def add_hint(hint_map, pos)
  valid_hint_pos = hint_map[pos] == NO_HINT
  if(valid_hint_pos)
    hint_map[pos] = HINT
  end
end