sub complete_shuffle
{
    my @sorted = @_;
    my @shuffled = ();
    my $niters = 0;
    my %shuff_used = ();
    for my $i ( 0 .. $#sorted ) {
        my $j = $i;
        while ( $j == $i or exists( $shuff_used{$j} )) {
            $j = int(rand(@sorted));
            $niters++;
        }
        $shuffled[$j] = $sorted[$i];
        $shuff_used{$j}++;
    }
    warn "complete shuffle finished in $niters iterations\n";
    return @shuffled;
}