Looks like your code had 2 loops, each counting to +6 million

foreach my $che (@b){
  @aa=split(/\s/,$che);

  foreach my $kh (@a){
    @bb=split(/\s/,$kh);

    for ($l=0;$l<=$#bb;$l++){
      for ($m=0;$m<=$#aa;$m++){

      ## this code executes 6 million x 6 million times
      if(($bb[$l] eq $aa[$m]) ){
      ..

      }
    }
  }
}

[download]

But within the 6 million words, there are only few thousand different ones so your loops were checking the same word thousand of times more than required. By holding the unique words from file1 in a hash you don't have to loop through 6 million words every time to find a match with a word from file2

poj

In reply to Re^11: compare two text file line by line, how to optimise by poj
in thread compare two text file line by line, how to optimise by thespirit

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