#! perl -slw
use strict;
use List::Util qw[ shuffle ];

our $N ||= 10;

my @people = map{ $_ . 'a', $_ . 'b' } 1 .. $N;

my $iters = 1; ## Just for testing
my @indices = shuffle 0 .. $#people;

++$iters, @indices = shuffle 0 .. $#people while grep{
    $indices[ $_ + 1] & 1                         ## If the upper item is odd
        ? $indices[ $_ ] +1 == $indices[ $_ + 1 ] ## the lower shouldn't be -1
        : $indices[ $_ ] == $indices[ $_ + 1 ] +1 ## vice versa
} 0 .. $#people/2;

@people = @people[ @indices ]; ## shuffle the real data

print "Took $iters iterations"; ## How many tries?

print "@people[ $_, $_+1 ]" for 0 .. $#people/2 if <STDIN>; ## Allows ^C