#! /usr/bin/perl -w
use strict;

my $last_n_gram = "";
my @line_numbers;
while (<>) {
    my ($n_gram, $line_number) = ($_ =~ /(.*): (\d+)$/);
    if ($n_gram ne $last_n_gram and @line_numbers) {
        @line_numbers = sort {$a <=> $b} @line_numbers;
        print "$last_n_gram: @line_numbers\n";
        $last_n_gram = $n_gram;
        @line_numbers = ();
    }
    push @line_numbers, $line_number;
}
@line_numbers = sort {$a <=> $b} @line_numbers;
print "$last_n_gram: @line_numbers\n";