Я думаю, что ваше предложение использовать хэш - это путь:
require 'set'
class Test
def initialize()
@lists = {174=>[1,2,3], 111=>[2,3,4], 160=>[2,4,5]}
end
def common_members(*keys)
lists_as_sets = {}
@lists.each_pair {|key,list| lists_as_sets[key] = list.to_set}
common = lists_as_sets[keys.shift] # Set to key[0] and nil that element of keys
keys.each {|k| common = common & lists_as_sets[k]} # Intersect the remaining keys, if any
common.to_a
end
end
t = Test.new
p t.common_members(174,111) # => [2,3]
p t.common_members(111,160) # => [2,4]
p t.common_members(174,111,160) # =>[2]