From: "Christoffer Lernö" <lerno@...>
Date: 2007-03-12T05:07:03+09:00
Subject: Re: [QUIZ] SimFrost (#117)

It's interesting that it looks like everyone populated their grid  
using a randomizer for each position in the grid.

This is is obviously fast, but for small grids (and low percentages),  
the percentage of actual generated vapour particles may be off by  
quite a bit.

For a 10x10 grid and 10% vapour, the amount of particles typically  
range between 5 and 15, which in turn makes the finished frost look  
very different from run to run.

I was thinking of ways to solve this. Obviously trying to randomly  
put vapour particles into an array - and retry if it already  
cointains vapur - is not ideal...

My best trick is this one:

require 'enumerator'
percentage = 30
width = 30
height = 20
vapour = width * height * percentage / 100
vacuum = width * height - vapour
grid = []
(Array.new(vacuum, ' ') + Array.new(vapour, '.')).sort_by  
{ rand }.each_slice(width) { |s| grid << s }

This gives us a grid that is guaranteed to have the correct initial  
proportion of vapour.

Anyone else with a more elegant solution to the problem?


Christoffer