Set up a practice session
- Create a pad, select JavaScript, and paste the exercise below. Use another language if that better fits your practice.
- Open the share menu and send the edit link to your partner. Agree on the session length using your own clock.
- Ask them to clarify the input and expected result before coding. Both people can point to code with live cursors.
- Open the private notes panel to record observations. These notes are separate from the shared files.
- Review the solution together and choose one concrete thing to practice next.
Try this exercise: the first repeated value
// Return the first value that appears more than once.
// Return null when all values are unique.
function firstDuplicate(values) {
// Explain your approach, then implement it.
}
// Examples to discuss:
// [3, 1, 3, 2] -> 3
// [1, 2, 2, 1] -> 2
// [] -> nullDiscuss whether values are always numbers, which duplicate should be returned, and what an empty input means. Ask your partner to trace the second example by hand before optimizing the solution.
Codepad does not run the solution or check tests. Verify execution in a local environment if it is part of your session.
A rubric you can put in private notes
| Observe | Record an example | Follow up |
|---|---|---|
| Clarification | Identified which duplicate comes first. | What should happen for empty input? |
| Reasoning | Explained a set-based or nested-loop approach. | How do time and space costs differ? |
| Correctness | Traced a repeated value and an all-unique case. | Can you find an input that breaks it? |
| Communication | Explained a revision while making it. | What would you improve with more time? |
Record what happened rather than a vague score. For example: “Asked whether the first duplicate means the first second occurrence; traced [1, 2, 2, 1] correctly.” This rubric is a practice aid, not a validated hiring assessment.
Know what the pad provides
You get collaborative editing, syntax highlighting, multiple file tabs, and private notes. There is no built-in code execution, call recording, interview playback, or applicant-tracking integration.
See the CoderPad comparison if you need a broader interview platform, or the sharing guide to send a read-only view after the session.
Keep the browser identity used for the session if you need to return to your private notes. The access guide explains what happens when cookies are cleared.