G'day jaiieq,

I appear to have identified more paths than you show (e.g. 0:6 6:12 12:24 is not in your list). Here's the code:

#!/usr/bin/env perl -l

use strict;
use warnings;

my %route_from;
my %routes_starting_at;
my @paths = qw{0:6 0:12 0:18 0:24 6:12 6:18 6:24 12:18 12:24 18:24};
map { push @{$route_from{$_->[0]}}, $_->[1] } map { [ split /:/ ] } @p
+aths;

for my $s (sort { $b <=> $a } keys %route_from) {
    for my $e (sort { $a <=> $b } @{$route_from{$s}}) {
        my $path = "$s:$e";

        if (exists $routes_starting_at{$e}) {
            for my $r (@{$routes_starting_at{$e}}) {
                my $ext_path = join ' ' => $path, $r;
                push @{$routes_starting_at{$s}}, $ext_path;
            }
        }
        else {
            push @{$routes_starting_at{$s}}, $path;
        }
    }
}

for my $k (sort { $a <=> $b } keys %routes_starting_at) {
    print for @{$routes_starting_at{$k}};
}
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Output:

$ pm_start_end_graph.pl
0:6 6:12 12:18 18:24
0:6 6:12 12:24
0:6 6:18 18:24
0:6 6:24
0:12 12:18 18:24
0:12 12:24
0:18 18:24
0:24
6:12 12:18 18:24
6:12 12:24
6:18 18:24
6:24
12:18 18:24
12:24
18:24
[download]