A derangement is just a mapping from every element of a set to some other element of the set. The simplest derangement is to map each element to its neighbor. And if you randomize the list before doing that mapping, you have a random derangement (mapping). You can then use that mapping on the original list to get a derangement of the original list. 
use strict;
use warnings;

my @array = (1..9);

sub derange {
  use List::Util 'shuffle';
  my @list = shuffle @_;
  my %map = map {($list[$_-1] => $list[$_])} 0..$#list;
  print "@map{@_}\n";
}

print "@array\n";
derange(@array) for 1..15;

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You'll see that in the output, no element appears in its original position (after the first line, which is there for reference).

One slightly non-obvious thing I did was to use negative indexing so that my mapping would wrap around from the last element to the first.

Caution: Contents may have been coded under pressure.

In reply to Re: Array Shuffle by Roy Johnson
in thread Array Shuffle by dunno260

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