[RuslanLomaka]

Summary

• Adds the Subsets (Power Set) problem under the Recursion & Backtracking topic (MEDIUM), slug subsets.
• New SubsetsProblem class in problem.algorithms, following BubbleSortProblem's exact pattern for metadata and hidden-test harness.
• The harness validates results order-independently: each returned subset is canonicalized (sorted by value) into a set and compared against the brute-force bitmask-generated expected power set, also checking the subset count equals 2^n with no duplicates.
• Registered the problem in ProblemRegistry's constructor.
• Added reference solutions src/test/resources/solutions/subsets.txt (iterative "double the subsets per element" approach) and subsets.wrong.txt (deliberately returns only single-element subsets, missing the empty subset and larger combinations).
• Bumped ProblemRegistryTest's hasSize(10) to hasSize(11).

Test plan

Ran the scoped validation command (also runs Checkstyle, bound to the validate phase):

./mvnw test -Dtest=HarnessVerificationTest,ProblemDefinitionContractTest,ProblemRegistryTest

Result:

[INFO] Running com.example.onlinejava.problem.ProblemRegistryTest
[INFO] Tests run: 7, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.270 s -- in com.example.onlinejava.problem.ProblemRegistryTest
[INFO] Running com.example.onlinejava.problem.HarnessVerificationTest
[INFO] Tests run: 22, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 8.186 s -- in com.example.onlinejava.problem.HarnessVerificationTest
[INFO] Running com.example.onlinejava.problem.ProblemDefinitionContractTest
[INFO] Tests run: 22, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.062 s -- in com.example.onlinejava.problem.ProblemDefinitionContractTest

[INFO] Results:
[INFO] Tests run: 51, Failures: 0, Errors: 0, Skipped: 0
[INFO] BUILD SUCCESS

Only the whitelisted files were touched (confirmed via git diff --name-only): the new problem class, ProblemRegistry.java, the two solution files, and ProblemRegistryTest.java.

Note that the repo's own CI (.github/workflows/ci-cd.yml) will independently re-run the full suite against a real Postgres container before merge is possible.

Opened automatically by a scheduled cloud agent (every 2 hours), not auto-merged -- please review.

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Run configuration

• Source mode: Auto
• Repository: RuslanLomaka/OnlineJavaSandbox
• Branch: problem/subsets
• File: .coderabbit.yaml
• Commit: 5b482fd
• Layers: Repository YAML
• Review profile: ASSERTIVE
• Plan: Advanced
• Run ID: ae561de9-5e73-4da0-b844-35b87cd5eccc

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud