[a8 b4 c1 d3 e6 f2 g7 h5]
[a9 b7 c4 d2 e8 f6 g1 h3 i5]

##</code><code>##

  N       Original         Faster       Non-Pure
  4           0.06           0.05           0.04
  5           0.07           0.04           0.05
  6           1.57           0.07           0.05
  7           9.29           0.06           0.05
  8                          0.23           0.06
  9                          0.16           0.06
 10                          0.50           0.07
 11                          0.41           0.07
 12                          2.64           0.14
 13                          1.58           0.10
 14                         37.23           0.82
 15                         35.45           0.70
 16                                         5.45
 17                                         3.18
 18                                        27.17
 19                                         1.89
 20                                             

##</code><code>##

#!/usr/bin/perl
            
use strict;
use warnings;
no warnings qw /syntax/;

$| = 1;

my $width    =  15;
my $time_out = 120;

my @cmds = ("./queens2 -n ",
            "./queens3 -n ",
            "./queens1 -f -n ");
my $nr_of_commands = @cmds;
            
my $N = 4;
print "  N";
printf "%${width}s" => $_ for qw /Original Faster Non-Pure/;
print "\n";
while ($nr_of_commands) {
    printf "%3d" => $N;
    foreach my $cmd (@cmds) {
        unless (defined $cmd) {
            print " " x $width;
            next;
        }
        local $SIG {ALRM} = sub {die "Time out!"};
        alarm ($time_out);
        eval {
            my $time = (`/usr/bin/time -f "%U" $cmd $N 2>&1`) [-1];
            alarm (0);
            chomp $time;
            printf "%$width.2f" => $time;
        }; 
        if ($@ && $@ =~ /Time out/) {
            undef $cmd; 
            $nr_of_commands --;
            print " " x $width;
        }
    }
    print "\n";
    $N ++;
}