http://www.perlmonks.org?node_id=481987

BrowserUk has asked for the wisdom of the Perl Monks concerning the following question:

Given 2 arrays of numbers, I want an efficient algorithm for "cancelling out". (There is probably a proper name for this, but I don't know it).

Most easily described by example. Given:

  • @a = ( 10, 20, 33, 45, 60 );
  • @b = ( 2, 5, 10, 12, 16, 23, 45 );

    I want to cancel values between the arrays to end up with:

  • @c = ( 5, 33 ); Please note that 5 does not appear in @a.
  • @d = ( 8, 23 ); And 8 does not appear in @b.

    Note. This is a trivial example. Both the sizes of the arrays and the values will be much larger.

    Update: This is not the elimination of duplicates or intersection of arrays. Once any duplicates have been eliminated, it then becomes a task of reducing factors from @a & @b unil no further factors can be removed.


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    2005-08-16 Retitled by Arunbear, as per Monastery guidelines
    Original title: 'Algorithm wanted'