Study Summary — April 26, 2026

LeetCode — Merge Sorted Array (Easy)

Key Concepts

• Merge two sorted arrays nums1 and nums2 in-place into nums1, which has extra space at the end to accommodate all elements

• Brute force (copy + sort) works but is O((m+n) log(m+n)) — wasteful since both arrays are already sorted

• Optimal approach: iterate backwards using three pointers — one at the end of each array's valid portion, and one at the last slot of nums1

• Compare from the back: place the larger of the two current elements at the tail, then decrement that pointer — avoids overwriting unprocessed elements

• Time: O(m+n), Space: O(1) — classic in-place merge pattern that appears in merge sort and many interview follow-ups

Professional Programming — Testing

• Testing Strategies in a Microservices Architecture — Martin Fowler

• Software Testing Anti-patterns — Kostis Kapelonis

Key Concepts

• Favour integration tests over pure unit tests in most production codebases — they catch more real-world failures

• Confirmation bias leads developers to write mostly positive test cases; deliberately test edge cases and failure modes

• Avoid common anti-patterns: testing implementation details, excessive mocking, and writing tests only after bugs appear

• Automated documentation tests ensure your README examples don't silently go out of date

• A good test suite is a safety net that enables confident refactoring — invest in it like production code

Claude Code Docs — Subagents

Key Concepts

• Subagents are specialized AI assistants that Claude Code can delegate tasks to, each with their own context window, tools, and system prompt

• Each subagent runs independently, preventing context pollution and keeping the main conversation focused on high-level goals

• Create subagents with /agents or by placing YAML-frontmatter markdown files in .claude/agents/

• Subagents can be granted access to specific built-in tools (Bash, Read, Write) or any MCP tools from connected servers

• Once created, subagents are reusable across projects and shareable with teammates for consistent workflows

ByteByteGo — 6 Software Architectural Patterns You Must Know

Key Concepts

• Layered: each layer has a clear role (presentation, business logic, data); easy to build quickly but can become unorganized without discipline

• Microservices: break a large system into small independent components; fault-tolerant and individually scalable, but adds operational complexity

• Event-Driven: services communicate by emitting events others may consume; promotes loose coupling but makes testing harder

• Client-Server: clients send requests, servers respond — the foundation of most networked applications and real-time services

• Plugin (Microkernel): a stable core system extended by independent plugin modules; great for tools like IDEs that need to grow over time without changing the core