From: "Schüle Daniel" <uval@...>
Date: 2006-07-31T08:10:07+09:00
Subject: Array#permutate

Hello,

this is my handmade Array#permutate function
are there any alternatives (maybe C extension modules)?
especially are there functions that would not create all
permutations and return them as one single memory consuming array
but give each one on demand?

Regards, Daniel

# arrayperm.rb

class Array
         def permutate
                 return self if [0,1].member? size
                 return [self, self.reverse] if size == 2
                 return  [[self[0],self[1],self[2]],
                          [self[0],self[2],self[1]],
                          [self[1],self[0],self[2]],
                          [self[1],self[2],self[0]],
                          [self[2],self[0],self[1]],
                          [self[2],self[1],self[0]]] if size == 3
                 ret = []
                 for perm in self[1..-1].permutate
                         for i in 0..perm.size
                                 ret.push( perm[0...i] + [first] + 
perm[i..-1] )
                         end
                 end
                 return ret
         end
end


irb(main):011:0* require "arrayperm"
=> true
irb(main):012:0> [1,2,3,4].permutate.size
=> 24
irb(main):013:0> [1,2,3,4].permutate.each{|perm| p perm};nil
[1, 2, 3, 4]
[2, 1, 3, 4]
[2, 3, 1, 4]
[2, 3, 4, 1]
[1, 2, 4, 3]
[2, 1, 4, 3]
[2, 4, 1, 3]
[2, 4, 3, 1]
[1, 3, 2, 4]
[3, 1, 2, 4]
[3, 2, 1, 4]
[3, 2, 4, 1]
[1, 3, 4, 2]
[3, 1, 4, 2]
[3, 4, 1, 2]
[3, 4, 2, 1]
[1, 4, 2, 3]
[4, 1, 2, 3]
[4, 2, 1, 3]
[4, 2, 3, 1]
[1, 4, 3, 2]
[4, 1, 3, 2]
[4, 3, 1, 2]
[4, 3, 2, 1]
=> nil
irb(main):014:0>