# reorder an array using only swap(ARRAY, X, Y),
# given a new set of indices

my @array = qw( put these in a different order );
my @order = qw( 1 3 5 4 2 0 );
reorder_swap(\@array, \@order);

# expected outcome:
# qw( these a order different in put )

sub reorder_swap {
  my ($a, $o) = @_;
  my @P = my @R = 0 .. $#$o;

  for (0 .. $#$o) {
    next if $P[$$o[$_]] == $_;
    swap($a, $P[$$o[$_]], $_);
    (@P[$R[$_],$$o[$_]], @R[$P[$$o[$_]],$_]) =
    (@P[$$o[$_],$R[$_]], @R[$_,$P[$$o[$_]]]);
  }
}

sub swap {
  my ($a, $x, $y) = @_;
  @$a[$x,$y] = @$a[$y,$x];
}