#!/usr/bin/perl

use strict;
use warnings;

my $maxw = 600; # 200
my $maxp = 612; # 600_000

sub uniq {
  my %uniq;
  @uniq{@_} = ();
  return keys %uniq;
} # uniq

print {*STDERR} "Generate fake paragraphs\n";
my @para = map [uniq map int(rand $maxw),0..int(rand $maxw)],1..$maxp;

print {*STDERR} "Sort\n";
@para = sort {@$a <=> @$b} @para;


print {*STDERR} "Count reversed hash\n";
my %words_in_para;
for(my $i=0;$i<=$#para;$i++){
  foreach my $word(@{ $para[$i] }){
    push @{ $words_in_para{$word} },$i;
  }
}

print {*STDERR} "Solving\n";
my $start_time = time();
my $i = 0;
while ($i <= $#para){
  my $para = $para[$i];

  unless(grep 1 == @{ $words_in_para{$_} },@$para){
    # all words appear somewhere else, delete the paragraph
    foreach my $word (@$para){
      $words_in_para{$word} = [ grep $_ ne $i,@{ $words_in_para{$word}
+ } ];
    }
    $para[$i] = [];
  }
  print {*STDERR} "$i/$maxp\r";
  $i++;
}

my $end_time = time();

print "\n";
print join "\n",map {'['.join(' ',sort {$a<=>$b} @$_).']'} grep @$_,@p
+ara;
print "\n";
print $end_time - $start_time,"s\n";
[download]