use strict;
use warnings;
use Data::Dump::Streamer;

my @arr = ([11, 22, [[]]], [333, 444, []], [6666, 7777, []]);

push @{$arr[0][2][0]}, 3;
Dump \@arr;

@arr = ([11, 22], [333, 444], [6666, 7777]);

push @{$arr[0][2][0]}, 3;
Dump \@arr;