code_challenge

Interview-prep workspace: LeetCode-style problem set, algorithm and data-structure reference code, and a full, targeted study pack for a Senior Software Development Engineer role at a healthcare client (referred to throughout as "TheClient").

Every Java file compiles standalone and opens with a block comment written for a junior engineer. Streaming and non-streaming implementations of the same idea are kept in sibling directories so you can compare them side by side.

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Directory map

code_challenge/
├── README.md                            ← you are here
├── docs/
│   ├── interview-strategy/              ← general interview tactics, pattern recognition
│   ├── theclient-interview/                   ← 10 topic files mapped to the TheClient JD
│   └── java-deep-dive/                  ← 14 Java / Spring topic essays
├── patterns/                            ← 6 warm-up problems + Java quick reference
├── algorithms/                          ← 21 algorithm patterns (Sliding Window, BFS, DP, ...)
│   └── streaming/                       ← streaming variants of 5 of them
├── data-structures/                     ← 11 foundational structures
│   └── streaming/                       ← streaming data-source + collector examples
├── problems/                            ← LeetCode-style drill set
│   ├── easy/                            ← 27 problems
│   ├── medium/                          ← 39 problems
│   └── hard/                            ← 4 problems
└── theclient-examples/                        ← compilable Java examples for the TheClient JD
    ├── kafka/                           ← producer, consumer, rebalance, schema evolution
    │   └── streaming/                   ← Kafka Streams windowed aggregation, Connect notes
    ├── spring-batch-etl/                ← HL7→FHIR migration + partitioned variant
    │   └── streaming/                   ← Spring Cloud Stream counterpart
    ├── fhir/                            ← HAPI FHIR Patient, Bundle transaction, v2→FHIR parser
    ├── observability/                   ← OpenTelemetry manual spans + SLO metrics
    └── security/                        ← OAuth2 + SMART scopes, PHI-redacting logger

Where to start

• LeetCode practice — start at patterns/ for a warm-up, then move to problems/easy/ and drill by theme using docs/interview-strategy/PATTERN_RECOGNITION.md.
• TheClient-specific prep — open docs/theclient-interview/README.md for the JD-requirement ↔ study-topic map. Each topic file links to the paired code under theclient-examples/.
• Java/Spring refresh — see docs/java-deep-dive/.

Conventions

Java code

• Style: Google Java Style Guide — 2-space indent, 100-char lines, braces on single-line if, one top-level class per file, UpperCamelCase classes / lowerCamelCase methods.
• Comments: a large block comment at the top of every standalone Java file written for a junior engineer. Inline // comments only where the "why" is non-obvious.
• Target: Java 17+.
• No Lombok. Everything you see is standard library + explicit Maven deps.
• Runnable offline: every main() runs without network / broker / DB access. Anything that would hit an external system is gated behind Boolean.getBoolean("liveRun") — set -DliveRun=true to exercise live.

Markdown docs

• Links: every reference link is on an authoritative source (hl7.org, spring.io, kafka.apache.org, opentelemetry.io, hhs.gov, cloud.google.com).
• Cross-links: topic docs link to their paired code. Code READMEs link back to the study card. Both link to the TheClient JD where relevant.
• Length: topic cards target 5-10 minute reads. Longer material lives in the deep-dive essays.

Repository layout rule

Where a topic has both a batch / snapshot form and a streaming form, the streaming form lives in a streaming/ subdirectory of the topic folder. This applies to algorithms/, data-structures/, theclient-examples/kafka/, and theclient-examples/spring-batch-etl/.

TheClient JD at a glance

The study pack under docs/theclient-interview/ is aligned to these required + preferred qualifications:

Required:

• 5+ yrs Java/JEE + Spring Boot + Spring Cloud + RESTful microservices
• 3+ yrs Apache Kafka (event streaming, partitions, consumer groups, schema registry)
• 3+ yrs CI/CD, Git workflows, automated testing
• 3+ yrs Docker, Kubernetes, cloud orchestration
• 2+ yrs cloud (GCP, AWS, Azure)

Preferred:

• FHIR, HL7 v2, SMART on FHIR, EHR integrations (Epic, Cerner, MEDITECH)
• GCP (GKE/Cloud Run, Cloud Build, IAM)
• Large-scale modernization / data platform migration
• Spring Batch, Dataflow, cloud-native ETL
• OAuth 2.0/OIDC, TLS, secrets management, scanning
• HIPAA, HITRUST, regulated healthcare environments

See docs/theclient-interview/README.md for the topic-by-topic mapping.

Prerequisites

• Java 17+ (pattern / problem files)
• Maven 3.9+ (TheClient example files have dependencies — see each subfolder's README)
• Docker + Docker Compose (optional, for the Kafka examples)

License

MIT — see LICENSE.