Re: Generating 0 .. N Randomly and Efficiently

This looks like shuffling a deck of cards. Wouldn't it be easier to create an array of the appropriate size, populate it, shuffle it, and then print the numbers?

#!/usr/bin/perl

use strict;
use warnings;

my $SIZE = 10;
my @a = (0..$SIZE);

for (@a) {
  my $i = int(rand($SIZE+1));
  ($a[$i],$a[$_])=($a[$_],$a[$i])
}

print "$_\n" for @a;
[download]

Hope this helped,
-v

"Perl. There is no substitute."

Comment on Re: Generating 0 .. N Randomly and Efficiently Download Code

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Re^2: Generating 0 .. N Randomly and Efficiently by Limbic~Region (Chancellor) on Oct 19, 2004 at 16:23 UTC
Velaki, Wouldn't it be easier... Yes of course, but that's not the point. The point is to learn new things by removing tools (memory) from the toolbox. Cheers - L~R	[reply]
Re^3: Generating 0 .. N Randomly and Efficiently by ikegami (Patriarch) on Oct 19, 2004 at 16:33 UTC
How does Velaki's solution use more memory (except maybe `for (@a)`, which could be replaced with `for ($j=0; $j<@a; $j++)`)? Update: Ah yes, you return an interator instead of building an actual list.	[reply] [d/l] [select]
Re^4: Generating 0 .. N Randomly and Efficiently by Limbic~Region (Chancellor) on Oct 19, 2004 at 16:37 UTC
ikegami, As you noted, the list is never constructed - there is only an iterator that finds the next randomly chosen number. Additionally, a bitstring is compact. If you wanted to generate 0 .. 80_000_000, it would create a bitstring only about 1 mb in size. Cheers - L~R	[reply]