require 'pp'

class Array
  def shuffle!( )
    each_index {|i| j = rand(i+1); self[i], self[j] = self[j], self[i]}
  end
  def shuffle( ) self.dup.shuffle! end
end

lists = (1..6).inject( [] ) { |m,o| m << [] }
( 1..50 ).to_a.shuffle.each { |x| lists[ rand(6) ] << x }

target = Integer( rand( 50 ) + 1 )
pp lists
list_no = nil
lists.each_index { |i| list_no = i if lists[i].any? { |x| x == target } }

puts "#{target} is in list #{list_no}"