Conway's Game of life

game_of_life.rb

# @param {Integer[][]} board
# @return {Void} Do not return anything, modify board in-place instead.
def game_of_life(board)
    m = board.size
    n = board[0].size
    meta_data = {}
    (0...m).each do |row|
      (0...n).each do |col|
        living_neighbours = live_neighbours(board, row, col)
        # meta-data format -> [row:col] => [old_value, num_of_live_neighbours]
        meta_data["#{row}:#{col}"] = [board[row][col], living_neighbours]
      end
    end

    (0...m).each do |row|
      (0...n).each do |col|
        meta = meta_data["#{row}:#{col}"]
        if meta[0].zero? # dead
          board[row][col] = 1 if meta[1] == 3
        else
          board[row][col] = ([2, 3].include?(meta[1]) ? 1 : 0)
        end
      end
    end
end

  def live_neighbours(board, row, col)
    result = 0
    result += 1 if cell_exists?(board, row, col - 1) && board[row][col - 1] == 1
    result += 1 if cell_exists?(board, row - 1, col-1) && board[row - 1][col - 1] == 1
    result += 1 if cell_exists?(board, row-1, col) && board[row - 1][col] == 1
    result += 1 if cell_exists?(board, row-1, col+1) && board[row - 1][col + 1] == 1
    result += 1 if cell_exists?(board, row, col+1) && board[row][col + 1] == 1
    result += 1 if cell_exists?(board, row+1, col+1) && board[row + 1][col + 1] == 1
    result += 1 if cell_exists?(board, row+1, col) && board[row + 1][col] == 1
    result += 1 if cell_exists?(board, row+1, col-1) && board[row + 1][col - 1] == 1
    result
  end

  def cell_exists?(board, row, col)
    return false if row >= board.size || row < 0
    return false if col >= board[0].size || col < 0
    true
  end