Java Interview Question: Remove Inactive Users Efficiently

Efficient User Cleanup in Large Datasets

Problem Description

Imagine you’re working on a user access control system for an application, and you need to clean up a list of users who have been marked as inactive. Your goal is to remove all inactive users (status = INACTIVE) from the list while keeping the operation efficient and minimizing memory usage.

The current solution creates a new list to store active users, which is memory inefficient for large lists.

• How would you modify the solution to improve memory usage by operating in place?
• What is the time complexity of your proposed solution, and how does it compare to the existing approach?

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Existing Approach

• The existing approach Iterates over each customer filters only the active ones and then maps it to a new array list.

    public static void main(String[] args) {
        List<Customer> customers = new ArrayList<>();
        Random random = new Random();
        IntStream.rangeClosed(1, 100_000_000).forEach(i -> {…