Tarun Y — R50-T025: Make verification repeatable for longestCommonSubsequence (LongestCommonSubsequence.js) [Dynamic-Programming/LongestCommonSubsequence.js] #25

Student: Tarun Y

Task: R50-T025 · 5 of 10
Repository: https://github.com/S-AI-Projects/TheAlgorithms-JavaScript
Assigned working branch: student/e26b07f0633

Goal

Work on Dynamic-Programming/LongestCommonSubsequence.js. Control the external state used while testing longestCommonSubsequence. For a pure function, verify repeated calls and input isolation; for time, randomness, network or UI code, inject or mock the relevant dependency. Fixture: Use the smallest valid input and one ordinary input for longestCommonSubsequence from Dynamic-Programming/LongestCommonSubsequence.js. Write the literal inputs and independently calculated expected outputs in the tests before editing the implementation. The check must name the source line establishing each precondition.

Steps

1. Read Dynamic-Programming/LongestCommonSubsequence.js, especially longestCommonSubsequence near line 30. Record its public inputs, result, mutation behavior and any external dependencies before changing it.
2. Identify every observable dependency used by this item; explicitly state when none exists.
3. Run the same fixture twice in fresh isolated state and once after another valid input; assert that earlier runs cannot alter the later result.
4. Implement work/R50-T025/check.py as a focused runner that executes the new checks and propagates failures. Native check to incorporate: run the repository test script in non-watch mode after installing from its lockfile; for browser-only code use a browser test instead of plain Node. Record the actual command and nonzero test count.
5. Create the checks specified below and run python3 work/R50-T025/check.py. Save inputs, expected versus actual results and tool versions in work/R50-T025/; a check must exit non-zero when an assertion fails.
6. Commit the repository change on branch R50-T025; prepare a PR to the organisation fork explaining the result and linking the checks. Keep each task independently reviewable. Remove work/R50-T025/ from a later upstream branch.

Done when

☐ The checked behavior is tied to longestCommonSubsequence in Dynamic-Programming/LongestCommonSubsequence.js; every assertion has an explicit expected value.
☐ Use the smallest valid input and one ordinary input for longestCommonSubsequence from Dynamic-Programming/LongestCommonSubsequence.js. Write the literal inputs and independently calculated expected outputs in the tests before editing the implementation. The check must name the source line establishing each precondition.
☐ Existing supported behavior and the public interface are preserved unless a failing regression demonstrates and documents a defect.
☐ The focused test works without live network access, a real user account or GUI interaction.
☐ Any introduced dependency parameter has a default preserving current callers.

Submission checklist

• Complete this task and its checks.
• Add the required evidence and link your pull request here.
• Select this S-AI-Projects fork as the PR base repository.
• Request instructor review.

Keep this PR focused on this task. Do not submit assignment PRs to the upstream repository.