All Unique Values Keep Order

Remove duplicates from a list while preserving the original order of first occurrences.

deduplicate order list hash-set

Write a function `unique_keep_order(lst)` that takes a list `lst` and returns a new list containing only the distinct elements of `lst`, in the order they first appear. 

For example, given `[3, 1, 3, 2, 1]`, the result should be `[3, 1, 2]`. The original list should not be modified. Your function must handle lists with 0 or more elements. Elements can be of any hashable type (e.g., integers, strings, tuples).

Constraints

0 <= len(lst) <= 10^5. The function should run in O(n) time and use O(n) extra space.

Example

>>> unique_keep_order([3, 1, 3, 2, 1])
[3, 1, 2]
>>> unique_keep_order(['a', 'b', 'a', 'c', 'b'])
['a', 'b', 'c']
>>> unique_keep_order([])
[]

10 points ~15 min

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Hints

Use a set to track which elements have already been seen.

Iterate through the list and only append an element to the result if it is not already in the set.

Remember to add each element to the set after checking/appending.

Test Results

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