package Sparse;

sub new {
    return bless [ [], [], [] ], $_[ 0 ];
}

sub populateFromFH {
    my( $self, $fh ) = @_;
    my( $a, $ia, $ja ) = @$self;
    push @{ $ia }, 0;
    while( <$fh> ) {
        my @n = split;
        my $first = 0;
        1 until $n[ $first++ ];
        my $len = --$first;
        1 while $n[ $len++ ];
        --$len;
        $len -= $first + 1;
        push @{ $a }, @n[ $first .. $first + $len ];
        push @{ $ja }, $first;
        push @{ $ia }, scalar @{ $a };
    }
}

sub getMN{
    my( $self, $m, $n ) = @_;
    my( $a, $ia, $ja ) = @$self;
    my $first = $ja->[ $m ];
    my $offset = $ia->[ $m ];
    my $len    = $ia->[ $m + 1 ] - $offset - 1;
    my @nonZeroN = @{ $a }[ $offset .. $offset + $len ];
    return 0 if $n < $first or $n > $first + $len;
    return $nonZeroN[ $n - $first ];
}

1;