# File lib/core/facets/array/permutation.rb, line 11 def permutation(n=size) if size < n or n < 0 elsif n == 0 yield([]) else self[1..-1].permutation(n - 1) do |x| (0...n).each do |i| yield(x[0...i] + [first] + x[i..-1]) end end self[1..-1].permutation(n) do |x| yield(x) end end end