Pythonbeginner

CODING EXERCISE

Find duplicates

Return the repeated values from a list while preserving their first repeated order.

Requirements

Return the expected value for every provided input.
Keep the solution readable and cover edge cases.
Avoid mutating the input unless the prompt requires it.

Example

Input

[
  1,
  2,
  1,
  3,
  2
]

Expected output

[
  1,
  2
]

Show a hint

Start with the simplest correct solution, then test an empty or minimal input.

local runtime

RUNTIME OUTPUT

Use your Python runtime locally, then compare with solution.py.

Use your local runtime, then review the reference solution

A PRACTICAL PLAN

Work through Find duplicates with intent.

Translate the contract.Turn the requirements into a short checklist before editing your-solution.py.
Use the example as evidence.Predict the result for the supplied input, then add one boundary case such as an empty value, a limit, or unexpected input.
Review the implementation.Compare your choices against solution.py only after a real attempt.

EXERCISE FAQ

Before you move on.

What does “Find duplicates” teach?

This beginner Python exercise focuses on Python. Its requirements define the exact behavior to implement before you write code.

How should I validate this Python solution?

Start with the displayed example input and expected output, then test a boundary case suggested by the requirements. Write and compile the starter in your local Python environment, exercise the example and edge cases, then compare your approach with solution.py.

When should I open the reference solution?

Attempt Find duplicates first. Then open the read-only solution file to compare the contract, edge-case handling, and implementation choices—not simply to copy the final code.

Find duplicates

Requirements

Example

Work through Find duplicates with intent.

Before you move on.

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