I am developing an app and I need to tackle a problem here.

The app is kind of an e-commerce app where each user will be shown a list of items daily. The problem is, I need to keep a track of all the items seen by a user so that those items are not shown again. 

How can I do this?

**Approach I**
Maintain the ids of all the items seen by a user in a cache and check the cache each time a GET API call comes from a user.

**Approach II**
Maintain a reverse mapping from item to user to avoid showing duplicate items.