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Author image Robin Houston


Algorithm::FastPermute - Rapid generation of permutations


  use Algorithm::FastPermute ('permute');
  my @array = (1..shift());
  permute {
      print "@array\n";         # Print all the permutations
  } @array;


Algorithm::FastPermute generates all the permutations of an array. You pass a block of code, which will be executed for each permutation. The array will be changed in place, and then changed back again before permute returns. During the execution of the callback, the array is read-only and you'll get an error if you try to change its length. (You can change its elements, but the consequences are liable to confuse you and may change in future versions.)

You have to pass an array, it can't just be a list. It does work with special arrays and tied arrays, though unless you're doing something particularly abstruse you'd be better off copying the elements into a normal array first.

It's very fast. My tests suggest it's four or five times as fast as Algorithm::Permute's traditional interface. If you're permuting a large list (nine or more elements, say) then you'll appreciate this enormously. If your lists are short then Algorithm::Permute will still finish faster than you can blink, and you may find its interface more convenient.

In fact, the FastPermute interface (and code) is now also included in Algorithm::Permute, so you may not need both. Enhancements and bug fixes will appear here first, from where (at Edwin Pratomo's discretion) they'll probably make their way into Algorithm::Permute.

The code is run inside a pseudo block, rather than as a normal subroutine. That means you can't use return, and you can't jump out of it using goto and so on. Also, caller won't tell you anything helpful from inside the callback. Such is the price of speed.

The order in which the permutations are generated is not guaranteed, so don't rely on it.


The permute function is exported by default.


Robin Houston, <robin@kitsite.com>

Based on a C program by Matt Day.




Copyright (c) 2001-2008, Robin Houston. All Rights Reserved. This module is free software. It may be used, redistributed and/or modified under the same terms as Perl itself.