Find All Duplicates

Python data engineering interview problem. Difficulty: beginner. Pattern: Arrays. About 10 minutes. Free to practice.

Find all values that appear twice; return sorted. Treat this as a production helper: match the contracted return shape, including empty and duplicate inputs.

A data load can contain ids that were sent twice. You need the ids that occur exactly twice, not every id that appears once. Find all values that appear twice in the list and return them in ascending order. Each value in the input appears once or twice, so a value is reported when its second occurrence is found. Write the function find_duplicates(nums: list) -> list. In [4, 3, 2, 7, 8, 2, 3, 1], the repeated values are 2 and 3, so the answer is [2, 3]. The starter file already has the function name and the harness print lines. Keep them, and fill only the function body.

Requirements

• Return every value that occurs twice.
• Return each repeated value once.
• Sort the result from smallest to largest.

Constraints

• The list has length n and every value is in 1 to n.
• Each value appears once or twice, and the return type is list.

Examples

Input: find_duplicates([4, 3, 2, 7, 8, 2, 3, 1]) Output: [2, 3] 2 and 3 appear twice.

Topics: lakebench, python, duplicates, range.

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