Graham,
You can save yourself an enormous number of headaches by simply
adding two more rows and columns to your array. For example, if you
wanted the world to be 80x24, make your array 82x26 and then make your
loops from 1..80 and 1..24. That way you can safely reference
cell[x-1][y-1] and cell[x+1][y+1] and you don't need all of your special
cases.
- Warren Brown
I'm aware this is a common approach, but I'm personally not found of it.
First of all, it confuses readers of the code. What size board are we really dealing with here? Why do these loops keep starting at 1 instead of 0?
Second, it almost always still requires special cases. For example, in the mentioned Game of Life, we must be sure organisms are not born into these border rows, or they'll change the results.
Finally, it's wasteful. I realize the memory is insignificant here, but it might not be in a bigger application.
My opinion is that it's better to address the real issue than just hide it away.
James Edward Gray II
On Sep 23, 2004, at 4:34 PM, Warren Brown wrote:
Graham,
You can save yourself an enormous number of headaches by simply
adding two more rows and columns to your array. For example, if you
wanted the world to be 80x24, make your array 82x26 and then make your
loops from 1..80 and 1..24. That way you can safely reference
cell[x-1][y-1] and cell[x+1][y+1] and you don't need all of your special
cases.
The 1 dimensional version of what you just described is how sqlite stores each row header. An array of num_fields+1 offsets where the last offset is the record length.
Pretty handy concept.
-Charlie
On Sep 23, 2004, at 2:34 PM, Warren Brown wrote:
Graham,
You can save yourself an enormous number of headaches by simply
adding two more rows and columns to your array. For example, if you
wanted the world to be 80x24, make your array 82x26 and then make your
loops from 1..80 and 1..24. That way you can safely reference
cell[x-1][y-1] and cell[x+1][y+1] and you don't need all of your special
cases.- Warren Brown
I agree with the spirit, but I would take it even farther. Why
bound the board at all? It should be a lot easier to just have an
infinite board (or at least, limited to Bignum#"max", whatever that
is). Easier, that is, after you reach in one ear, grab your brain, and
give it a sharp twist (about 0.76 radians to the NW should do it if
you've been coding in C).
A sketch:
WARNING: THIS CODE WAS TYPE IN MAIL AND HAS NEVER BEEN RUN
class A_cell
attr_accessor(
:state, # :filled or :empty
:neighbors, # 0..8
:loc # [x,y]
)
def initialize(x,y)
@state = :empty
@neighbors = 0
@loc = [x,y]
end
def fate
#depending on @state & @neighbors, return :filled or :empty
end
end
class A_board
attr_reader :cells # a hash of [x,y] => A_cell
def initialize
@cells = Hash.new
end
def step
update_neighbor_count
update_states
end
def update_neighbor_counts
@cells.keys.each { |x,y|
if @cells[[x,y]].state.filled
((x-1)..(x+1)).each { |x0|
((y-1)..(y+1)).each { |y0|
@cells[[x0,y0]] ||= A_cell.new(x0,y0)
@cells[[x0,y0]].neighbors += 1 unless
x0 == x and y0 == y
}
}
end
}
end
def update_states
@cells.keys.each { |x,y|
case @cells[[x,y]].fate
when :filled
@cells[[x,y]].state = :filled
@cells[[x,y]].neighbors = 0
when :empty
@cells.delete_at [x,y]
end
end
end
This has some fat & may be missing some details, but at least it should
give you the idea.
-- Markus
On Thu, 2004-09-23 at 14:34, Warren Brown wrote:
Graham,
You can save yourself an enormous number of headaches by simply
adding two more rows and columns to your array. For example, if you
wanted the world to be 80x24, make your array 82x26 and then make your
loops from 1..80 and 1..24. That way you can safely reference
cell[x-1][y-1] and cell[x+1][y+1] and you don't need all of your special
cases.
[snip]
class A_cell
attr_accessor(:state, # :filled or :empty
:neighbors, # 0..8
:loc # [x,y])
def initialize(x,y)
@state = :empty
@neighbors = 0
@loc = [x,y]
end
def fate
#depending on @state & @neighbors, return :filled or :empty
end
endclass A_board
attr_reader :cells # a hash of [x,y] => A_cell
def initialize
@cells = Hash.new
end
def step
update_neighbor_count
update_states
end
def update_neighbor_counts
@cells.keys.each { |x,y|
if @cells[[x,y]].state.filled
((x-1)..(x+1)).each { |x0|
((y-1)..(y+1)).each { |y0|
@cells[[x0,y0]] ||= A_cell.new(x0,y0)
@cells[[x0,y0]].neighbors += 1 unless
x0 == x and y0 == y
}
}
end
}
end
def update_states
@cells.keys.each { |x,y|
case @cells[[x,y]].fate
when :filled
@cells[[x,y]].state = :filled
@cells[[x,y]].neighbors = 0
when :empty
@cells.delete_at [x,y]
end
end
endThis has some fat & may be missing some details, but at least it should
give you the idea.-- Markus
I have also made a gameoflife implementation.. it looks like this
bash-2.05b$ expand -t2 gameoflife.rb
module GameOfLife
def determine_destiny(alive, count)
unless alive
return (count == 3)
end
(count == 2) or (count == 3)
end
def get(cells, y, x)
return 0 if x < 0 or y < 0
return 0 if y >= cells.size
row = cells[y]
return 0 if x >= row.size
row
end
def count_neighbours(cells, x, y)
n = 0
n += get(cells, y-1, x-1)
n += get(cells, y-1, x)
n += get(cells, y-1, x+1)
n += get(cells, y, x-1)
n += get(cells, y, x+1)
n += get(cells, y+1, x-1)
n += get(cells, y+1, x)
n += get(cells, y+1, x+1)
n
end
def lifecycle(cells)
y = 0
next_cells = cells.map do |row|
x = 0
next_row = row.map do |cell|
n = count_neighbours(cells, x, y)
x += 1
determine_destiny((cell != 0), n) ? 1 : 0
end
y += 1
next_row
end
next_cells
end
end
if $0 == __FILE__
puts "lets play a game"
class Game
include GameOfLife
def initialize
@cells = [
[0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0],
[0, 0, 1, 1, 1, 0],
[0, 1, 1, 1, 0, 0],
[0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0]
]
end
def next
@cells = lifecycle(@cells)
end
def inspect
rows = @cells.map do |row|
row.join(" ")
end
rows.join("\n")
end
end
game = Game.new
loop do
p game
gets
game.next
end
end
bash-2.05b$
On Friday 24 September 2004 06:25, Markus wrote:
--
Simon Strandgaard
This has some fat & may be missing some details, but at least it
should
give you the idea.
It doesn't seem to have much fat from my position. I appreciate the
time you (and others) have spent on this query. Thanks for the help.
I'll get on and remodel my version ASAP.
Thx to all for their assistance.
Regards
Graham