sub new
{
    my $class = shift;
    my ($max_rows) = @_;

    my $self = bless {
        max_rows => $max_rows,
        data => [],
    }, $class;
}

sub add_column
{
    my $self = shift;
    push @{$self->{data}}, [];
}

sub add_value
{
    my $self = shift;
    my ($x, $y, $value) = @_;

    return unless $x <= $max_rows;
    return unless $x >= 0;

    $self->{data}[$y][$x] = $value;
}

sub get_value
{
    my $self = shift;
    my ($x, $y) = @_;

    return $self->{data}[$y][$x];
}