• The Question

Write a function that takes a list of integers and returns a new list containing only the unique values in the same order as they first appeared.

• Extra Details

The function should not use built-in methods that automatically remove duplicates. You must implement the logic manually. The input list may contain positive numbers, negative numbers, or zeros.

• Optional Options

A. Use a loop and an additional data structure to track seen values.

B. Use recursion to build the list of unique elements.

C. Implement the solution using list comprehension only.

D. Solve it with time complexity O(n²).