use Data::Dump qw/pp/;

@array = (10, 11, 12, 2, 3, 4, 7);

@a = sort {$a <=> $b} @array;

$first = $last = shift @a;       # init start
push @a,"inf";                   # infinity end

for $now (@a) {
  unless ( $last+1 == $now ) {
    push @ranges,[$first,$last]; # todo: one element ranges
    $first=$now;
  }
  $last=$now;
}

pp @ranges;