Use a hash.
#!/usr/bin/perl
use strict;
use warnings;
my @array = (1,5,6,7,8,55,63,77,89,103,104,105,106,200,215,554);
my %free_numbers = map {$_ => 1} @array;
for my $number (@array)
{
my $ok = 1;
for (my $i = 0; $i < 4; $i++)
{
if (! exists $free_numbers{$number + $i})
{
$ok = 0;
last;
}
}
if ($ok)
{
print "found consecutive numbers: ";
for (my $i = 0; $i < 4; $i++)
{
print $number + $i, " ";
delete $free_numbers{$number + $i};
}
print "\n";
}
}
__END__
found consecutive numbers: 5 6 7 8
found consecutive numbers: 103 104 105 106