$length = 5; #Set to the size of derangment
my @results = &combinations(1..$length);

$comb = 0;
foreach (@results) {
    $found = 0;
    foreach my $num (1..$length){
        if(@$_[$num-1] == $num) {$found = 1;} #If true then not a dera
+ngement
    }
    if($found == 0) {print "@$_\n";$comb++;}
}
print "Number of derangements: $comb\n";

sub combinations {
  my @array = @_;
  if ($#array == 0) {return [ $array[0] ]; }
  my @results;
  my $element;
  foreach $element (0..$#array) {
    my @leftovers = @array;
    my $chosen_one = splice(@leftovers, $element, 1);
    foreach (&combinations(@leftovers)) {
      push(@results, [ $chosen_one, @{$_} ]);
    }
  }
  return @results;
}
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