From: "F. Senault" <fred@...>
Date: 2007-03-12T06:50:07+09:00
Subject: Re: [QUIZ] SimFrost (#117)

Le 11 mars 2007 � 21:07, Christoffer Lern� a �crit :

> Anyone else with a more elegant solution to the problem?

I'd use this (only moderately tested) :

#! /usr/local/bin/ruby

p = 0.3
w = 100
h = 100
t = h * w
v = (t * p).floor

g = Array.new(v, '.') + Array.new(t - v, '.')

0.upto(t - 1) do |i|
  j = i + rand(t - i)
  z = g[j] ; g[j] = g[i] ; g[i] = z
  # g[j], g[i] = g[i], g[j]
end

(And then split the grid in w chunks.)

The fun part is that the version using a parallel assignment (commented)
is actually much slower (about two times) than the version using the
temporary variable, to the point that it was beaten by sort_by (which is
supposed to be O(n*log(n)) versus O(n) for my versions).

200*200 :
                          user     system      total        real
scramble / temp :    15.281250   0.000000  15.281250 ( 15.587794)
scramble / swap :    31.398438   0.007812  31.406250 ( 32.220921)
sort_by rand :       28.625000   0.101562  28.726562 ( 29.168337)

500*500 :
                          user     system      total        real
scramble / temp :    97.195312   0.000000  97.195312 ( 98.037395)
scramble / swap :   297.937500   0.929688 298.867188 (302.746914)
sort_by rand :      213.906250   0.468750 214.375000 (217.172667)

Fred
-- 
Young at heart an' it gets so hard to wait
When no one I know can seem to help me now
Old at heart but I mustn't hesitate
If I'm to find my way out                     (Guns n' Roses, Estranged)