Discussion on: How to reduce the time complexity of nested loops

Thanks! That's one of the best descriptions of O() notation I've ever read.

However, can you please elaborate on the following example?

users_idx = {}

for user in users
  users_idx[user[:group_id]] = ...
end

for group in groups
  user_information = users_idx[group[:id]]
  # do something with group AND user information
end

What is the relation of users and groups in your example? Many-to-many or many-to-one?

What is saved in the index? All users who belong to a particular group? Or a single user who belongs to a particular group?