Copied this really nice permutation addon to the Array class.
class Array
def perm(n = size)
if size <>
elsif n == 0
yield([])
else
self[1..-1].perm(n - 1) do |x|
(0...n).each do |i|
yield(x[0...i] + [first] + x[i..-1])
end
end
self[1..-1].perm(n) do |x|
yield(x)
end
end
end
end
