Study Summary — April 27, 2026

LeetCode — Best Time to Buy and Sell Stock with Transaction Fee (Medium)

Key Concepts

• You are given an array prices where prices[i] is the stock price on day i, and an integer fee representing the transaction fee per trade.

• The goal is to maximize your profit by choosing when to buy and sell, with the constraint that you pay a fee each time you sell.

• State machine DP approach: Track two states — cash (max profit when not holding stock) and hold (max profit when holding stock). Transition: cash = max(cash, hold + prices[i] - fee) and hold = max(hold, cash - prices[i]).

• Greedy insight: You can make as many transactions as you like, but the fee discourages unnecessary trades — the DP naturally filters out unprofitable ones.

• Time complexity O(n), Space O(1) — single pass through the array with only two variables.

Professional Programming — Documentation

• Diátaxis: A systematic framework for technical documentation — breaks docs into tutorials, how-to guides, reference, and explanation

• Write the Docs: Software Documentation Guide — community-driven best practices for writing great docs

• Architecture Decision Records (ADRs) — lightweight way to capture and communicate important architectural decisions

Key Concepts

• The Diátaxis framework teaches that documentation serves four distinct user needs: learning (tutorials), doing (how-to guides), understanding (explanation), and referencing (technical reference). Mixing these modes creates confusing docs.

• Write documentation first, then code — treating docs as a first-class artifact (not an afterthought) leads to better-designed APIs and clearer thinking about what you are building.

• Architecture Decision Records (ADRs) provide a structured way to document why a decision was made, not just what was decided — invaluable for onboarding and future debugging.

• Automate documentation testing — code samples in docs rot quickly; tools like doctest, pytest, and CI checks ensure examples stay accurate over time.

• Audience-first thinking — always ask: is this for a new user learning the system, an experienced user looking up a detail, or someone trying to understand the design? Tailor accordingly.

Claude Code Docs — IDE Integrations

Key Concepts

• Native IDE support — Claude Code integrates directly into VS Code and JetBrains IDEs (IntelliJ, PyCharm, WebStorm, etc.), letting you run Claude commands without leaving your editor.

• Inline diff views — when Claude edits files, the IDE shows a standard diff view so you can review, accept, or reject changes file-by-file or hunk-by-hunk, just like a code review.

• Diagnostics context — Claude Code can read IDE diagnostics (errors, warnings, lint issues) from your editor and use them as context when generating fixes, making its suggestions more accurate.

• Terminal integration — the Claude Code CLI runs in the integrated terminal; the IDE extensions wire up keyboard shortcuts and sidebar panels so you can trigger sessions, approve tool use, and view output inline.

• MCP server connections via IDE — you can configure MCP servers through your IDE settings or claude_desktop_config.json, giving Claude Code access to custom tools scoped to a workspace or project.

ByteByteGo — CI/CD Pipeline Explained in Simple Terms

Key Concepts

• CI (Continuous Integration) means every code change is automatically built and tested the moment it is pushed — catching integration bugs early before they compound.

• CD (Continuous Delivery/Deployment) extends CI by automatically moving validated code through staging and into production, reducing release friction and enabling smaller, safer deploys.

• Pipeline stages typically follow: Source → Build → Test → Staging Deploy → Smoke Test → Production Deploy, with each stage acting as a quality gate that blocks bad code from advancing.

• Fast feedback loops are the core goal — a pipeline should tell a developer within minutes whether their change broke something, not hours or days later when context is lost.

• Infrastructure as Code (IaC) + CI/CD work together: tools like Terraform and GitHub Actions let you version, test, and automatically apply infrastructure changes the same way you manage application code.