# Use a set called seen and a list called unique to deduplicate ids while preserving order

Canonical URL: <https://datadriven.io/problems/use-a-set-called-seen-and-a-list-called-unique-to-deduplicat-e1d8e110>

Domain: Python · Difficulty: medium

## Problem

Use a set called seen and a list called unique to deduplicate ids while preserving order. Loop through ids: if an id is not in seen, add it to seen and append it to unique. Print the unique list, then its length.

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