#! perl -slw
use strict;
use Data::Dump qw[ pp ];

sub fillLTM {
    my @lt;
    my $n = 1;
    push @lt, [ splice @_, 0, $n++ ] while @_;
    return @lt;
}

## read raw data
while( my $rawData = <DATA> ) {
    ## Populate LT matrix
    my @lt = fillLTM( split ' ', $rawData );
    pp \@lt;;

    ## Pad to square matrix
    push @{ $lt[$_] }, (0)x( @{ $lt[-1] } - @{ $lt[$_] } ) for 0 .. $#lt -1;;
    pp \@lt;;
}

__DATA__
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

##</code><code>##

C:\test>junk
[
    [1],
    [2, 3],
    [4, 5, 6],
    [7, 8, 9, 10]
]
[
    [1, 0, 0, 0],
    [2, 3, 0, 0],
    [4, 5, 6, 0],
    [7, 8, 9, 10]
]

[
    [1],
    [2, 3],
    [4, 5, 6],
    [7, 8, 9, 10],
    [11, 12, 13, 14, 15]
]

[
    [1, 0, 0, 0, 0],
    [2, 3, 0, 0, 0],
    [4, 5, 6, 0, 0],
    [7, 8, 9, 10, 0],
    [11, 12, 13, 14, 15]
]