使用时间线存储数据范围的数据结构

Question

I need to store the activity log data for users in my application. It includes the the time when the user started doing an activity. For eg, at 1 PM, the started 'Activity A'. At 2 PM, the user started 'Activity B'. At 3 PM, the user started 'Avtivity A'. From these logs, I should later be able to query information like

1. How long was the user doing Activity A between 12 AM to 8 PM?
2. How many times did the user switch activities etc.

Can anyone suggest what would be a good in-memory data structure to store such information?

Edit: There could be thousands of logs. A user can't do multiple activities at the same time.

Answer 1

First, let's try to have a data structure for you to make the query assuming you have a single activity.

So let's have a list to store the timestamps (I am considering an integer example).

ArrayList<Integer> integers = new ArrayList<Integer>();

In this, you can store the timestamps. Let's say you have stored

integers.add(1);
integers.add(10);
integers.add(12);
integers.add(176);
integers.add(1678);

Now you need to way to access the only specific set of values in it. Consider the NavigableSet class from JDK.

NavigableSet<Integer> set = new TreeSet<>(integers);

You can query specific set using

set.subSet(0, 175); // this will give 1,10,12 from the above values

Now Have a map to store multiple Activities.

Map<String, List> activityTimeStampmap= new HashMap<>();

You can add Activity if it does not exist, You have to update the list if Activity Already exists.

Hope this helps you.