sub fisher_yates_shuffle {
        my $array = shift;
        my $i;
        for ($i = @$array; --$i; ) {
            my $j = int rand ($i+1);
            next if $i == $j;
            @$array[$i,$j] = @$array[$j,$i];
        }
    }

    my $N = 50;
    my @array = (1..$N);
    fisher_yates_shuffle( \@array );    # permutes @array in place

    print "@array";