Software Engineer's Blog — jamongx

Coding Interview

Jason Yang · 04 Aug, 2026

Longest Repeating Character Replacement (LeetCode 424): why a window is valid when its length minus its most-frequent letter stays within k, solved in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Pacific Atlantic Water Flow (LeetCode 417): flip the flow and DFS inward from each ocean's border, then intersect the two reachable sets. Java solution.

Coding Interview

Jason Yang · 04 Aug, 2026

Sum of Two Integers (LeetCode 371): add two numbers using only XOR and AND. Here's why XOR is the sum, AND is the carry, and how the loop lands in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Top K Frequent Elements (LeetCode 347): count with a hash map, then beat the O(n log n) bound by bucketing values by frequency for an O(n) answer in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Counting Bits (LeetCode 338): why dp[i] = dp[i >> 1] + (i & 1) counts set bits in one linear pass, plus the built-in baseline it beats — in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Number of Connected Components (LeetCode 323) in Java: count merges instead of nodes with Union-Find, or flood-fill each unvisited node with DFS.

Coding Interview

Jason Yang · 04 Aug, 2026

Coin Change (LeetCode 322): why grabbing the biggest coin fails, and the bottom-up DP that finds the fewest coins for an amount in O(amount × coins) — in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Longest Increasing Subsequence (LeetCode 300): the O(n^2) DP for the intuition, then the O(n log n) patience-sorting trick with binary search, in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Serialize and Deserialize Binary Tree (LeetCode 297): why a preorder walk with explicit null markers round-trips any tree, coded cleanly in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Find Median from Data Stream (LeetCode 295): balance a max-heap and a min-heap so the median sits at the top, with O(log n) inserts in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Encode and Decode Strings (LeetCode 271): why a delimiter alone can't work, and the length-prefix codec that round-trips any characters in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Alien Dictionary (LeetCode 269): turn a sorted word list into a character graph, then topologically sort it with Kahn's BFS in Java — cycles and prefixes included.

Coding Interview

Jason Yang · 04 Aug, 2026

Missing Number (LeetCode 268): why XOR-ing every index with every value leaves exactly the missing one, plus the Gauss-sum alternative, in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Graph Valid Tree (LeetCode 261): a tree is a connected, acyclic graph with exactly n-1 edges — solve it with union-find cycle detection in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Meeting Rooms II (LeetCode 253): find the minimum rooms by tracking peak overlap — the min-heap solution and the sweep-line trick, both in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Meeting Rooms (LeetCode 252): sort intervals by start, then one pass reveals whether any two overlap. Java code, the strict-vs-equal trap, and complexity.

Coding Interview

Jason Yang · 04 Aug, 2026

Valid Anagram (LeetCode 242): why a 26-slot frequency count beats sorting, the one-array Java solution, and how the Unicode follow-up changes the answer.

Coding Interview

Jason Yang · 04 Aug, 2026

Lowest Common Ancestor of a BST (LeetCode 235): use the sorted-order property to walk down until the two targets split, an O(h) one-pass solution in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Kth Smallest Element in a BST (LeetCode 230): why an inorder walk visits values in sorted order, so the kth node you touch is the answer — solved in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Invert Binary Tree (LeetCode 226): swap every node's children with a three-line recursion, plus the iterative BFS version and the null base case that matters.

Coding Interview

Jason Yang · 04 Aug, 2026

Word Search II (LeetCode 212): why one shared Trie beats running Word Search once per word, plus the backtracking DFS and pruning tricks, in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Design Add and Search Words (LeetCode 211): store words in a trie, then DFS through it so a '.' wildcard can branch into every child. Java solution explained.

Coding Interview

Jason Yang · 04 Aug, 2026

Implement Trie (LeetCode 208): build a prefix tree in Java where each node branches 26 ways, so insert, search, and startsWith all run in O(word length).

Coding Interview

Jason Yang · 04 Aug, 2026

Course Schedule (LeetCode 207): the whole problem is 'does this directed graph have a cycle?' Solve it with Kahn's topological sort in Java, plus the DFS alternative.

Coding Interview

Jason Yang · 04 Aug, 2026

Reverse Linked List (LeetCode 206): the three-pointer flip that reverses a singly linked list in place, plus the recursive version and why order matters.

Coding Interview

Jason Yang · 04 Aug, 2026

Number of Islands (LeetCode 200): count connected land groups with a DFS flood fill that sinks each island as it's found, in clean idiomatic Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Number of 1 Bits (LeetCode 191): counting set bits with a plain shift loop, then Brian Kernighan's n & (n-1) trick that only loops once per set bit — in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Reverse Bits (LeetCode 190): peel the low bit, stack it onto the result 32 times, and the >>> vs >> shift nuance in Java. Plus the byte-cache follow-up.

Coding Interview

Jason Yang · 04 Aug, 2026

Reorder List (LeetCode 143): interleave a linked list front-to-back in O(1) space by combining three classic pointer moves — find the middle, reverse, merge.

Coding Interview

Jason Yang · 04 Aug, 2026

Linked List Cycle (LeetCode 141): why two pointers moving at different speeds must collide inside a loop, and the O(1)-space Floyd's algorithm in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Word Break (LeetCode 139): why a greedy longest-match fails, how prefix DP with dp[i] = 'is s[0..i) segmentable' fixes it, and the prefix-DP Java solution.

Coding Interview

Jason Yang · 04 Aug, 2026

Clone Graph (LeetCode 133): why a single HashMap from original to copy solves cycles and shared neighbors at once, with a clean DFS solution in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Binary Tree Maximum Path Sum (LeetCode 124): why one DFS returns a single-branch gain to the parent while tracking a global best that bends through a node.

Coding Interview

Jason Yang · 04 Aug, 2026

Construct Binary Tree from Preorder and Inorder Traversal (LeetCode 105): why preorder hands you the root and inorder splits left from right, in O(n) Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Maximum Depth of Binary Tree (LeetCode 104): the one-line DFS recurrence, why depth is 1 + the taller subtree, and a BFS alternative in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Binary Tree Level Order Traversal (LeetCode 102): the queue-based BFS, why snapshotting the queue size groups each level, and clean Java code.

Coding Interview

Jason Yang · 04 Aug, 2026

Same Tree (LeetCode 100): compare two binary trees for identical shape and values with a four-line recursion, plus the iterative queue version and its traps.

Coding Interview

Jason Yang · 04 Aug, 2026

Validate Binary Search Tree (LeetCode 98): why checking a node against its children fails, and the min/max bounds recursion that fixes it in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Decode Ways (LeetCode 91): the Fibonacci-shaped count recurrence, why leading zeros kill a decoding, and the clean O(1)-space DP in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Word Search (LeetCode 79): how DFS plus in-place marking walks the grid, why you restore each cell on the way out, and the clean Java backtracking solution.

Coding Interview

Jason Yang · 04 Aug, 2026

Set Matrix Zeroes (LeetCode 73): why an in-place mark-then-sweep needs the matrix's own first row and column as scratch, plus the O(1)-space Java code.

Coding Interview

Jason Yang · 04 Aug, 2026

Unique Paths (LeetCode 62): why each grid cell is the sum of the ways from above and from the left, plus the O(n)-space rolling DP solution in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Insert Interval (LeetCode 57): why an already-sorted list lets you insert in one linear pass — the before / merge / after sweep in Java, no sorting needed.

Coding Interview

Jason Yang · 04 Aug, 2026

Merge Intervals (LeetCode 56): sort by start, then sweep once and extend the last interval whenever the next one overlaps — the Java sort-and-merge template.

Coding Interview

Jason Yang · 04 Aug, 2026

Jump Game (LeetCode 55): why one greedy pass tracking the farthest reachable index beats the O(n^2) DP, and why a trailing zero is the real trap, in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Spiral Matrix (LeetCode 54): walk the grid clockwise by tracking four edges and peeling one row or column off after each pass — clean Java, no visited set.

Coding Interview

Jason Yang · 04 Aug, 2026

Group Anagrams (LeetCode 49): pick a canonical key so every anagram hashes to the same bucket. Sorted-key vs count-array key in Java, with complexity.

Coding Interview

Jason Yang · 04 Aug, 2026

Rotate Image (LeetCode 48): why transpose-then-reverse rotates a matrix 90° clockwise in place, with the O(1)-space Java solution and the index math behind it.

Coding Interview

Jason Yang · 04 Aug, 2026

Combination Sum (LeetCode 39): why passing the same start index lets you reuse numbers, plus a sorted-and-pruned backtracking solution in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Merge k Sorted Lists (LeetCode 23): why merging one list at a time is O(n·k), and how a min-heap or pairwise merging cuts it to O(n log k) in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Merge Two Sorted Lists (LeetCode 21): the dummy-head trick that removes every empty-list special case, plus the O(1)-space splice solution in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Valid Parentheses (LeetCode 20): why a stack is the natural fit for matching brackets, a clean Java solution, and the empty-stack edge cases interviewers probe.

Coding Interview

Jason Yang · 04 Aug, 2026

Remove Nth Node From End of List (LeetCode 19): why a two-pointer gap lets you delete the nth-from-last node in one pass, plus the dummy-head trick in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Longest Palindromic Substring (LeetCode 5): why expanding around each center beats the DP table, the two-center trick for even lengths, and clean Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Advanced graphs in Java need named algorithms: Dijkstra for weighted shortest paths, Prim/Kruskal for a spanning tree, Bellman-Ford, and topological sort.

Coding Interview

Jason Yang · 04 Aug, 2026

Math and geometry problems in Java split two ways: manipulating a matrix in place with careful index arithmetic, and simulating arithmetic without overflow.

Coding Interview

Jason Yang · 04 Aug, 2026

Bit manipulation in Java rests on a few identities: XOR to cancel pairs, n & (n-1) to strip the lowest set bit, and shifts to add without a plus sign.

Coding Interview

Jason Yang · 04 Aug, 2026

2D DP in Java: when state needs two indices — two strings, a grid, or a mode — reading the recurrence from neighbor cells and rolling the table to O(n) space.

Coding Interview

Jason Yang · 04 Aug, 2026

A trie makes prefix a first-class query in Java: insert and startsWith in O(word length), wildcard matching, and a prefix tree that prunes a grid word search.

Coding Interview

Jason Yang · 04 Aug, 2026

Interval problems in Java almost all start by sorting, then one sweep: what to sort by, the overlap test, and counting concurrent intervals for room counts.

Coding Interview

Jason Yang · 04 Aug, 2026

Backtracking is a decision-tree DFS with an undo step. The choose/explore/unchoose template in Java, pruning dead branches, and the duplicate-skipping trick.

Coding Interview

Jason Yang · 04 Aug, 2026

Heap patterns in Java: the size-k trick for top-k, two heaps for a running median, and why a priority queue beats sorting when you only need the extreme.

Coding Interview

Jason Yang · 04 Aug, 2026

Stacks do two interview jobs in Java: matching what you must resolve later (parentheses, RPN), and the monotonic stack that finds next-greater in one O(n) pass.

Coding Interview

Jason Yang · 04 Aug, 2026

House Robber II (LeetCode 213): the circular twist solved by running the linear House Robber twice — once excluding the first house, once the last — in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

House Robber (LeetCode 198): the take-or-skip recurrence, why you can't rob adjacent houses, and the O(1)-space rolling solution in Java.

Coding Interview

Jason Yang · 04 Aug, 2026

Climbing Stairs (LeetCode 70): why the answer is Fibonacci, the memoized and bottom-up solutions in Java, and the rolling trick that drops it to O(1) space.

Coding Interview

Jason Yang · 04 Aug, 2026

Linked list problems in Java are three pointer moves: the dummy head, fast and slow pointers, and in-place reversal — plus the one that's a data structure.

Coding Interview

Jason Yang · 03 Aug, 2026

Most graph interview problems are disguised — grids, prerequisites, connectivity. How to spot them, the visited set trees never needed, and BFS vs DFS in Java.

Coding Interview

Jason Yang · 03 Aug, 2026

Binary tree problems in Java are recursion plus the right traversal: pre/in/post-order DFS vs BFS, what each recursive call returns, and the BST in-order trick.

Coding Interview

Jason Yang · 03 Aug, 2026

Arrays and hashing in Java: how a hash set or map trades memory for O(1) lookups to turn O(n^2) scans linear, and when hashing is the wrong reflex.

Coding Interview

Jason Yang · 03 Aug, 2026

Greedy algorithms are quick to write and often wrong. How to tell when the greedy choice is provably optimal, the exchange argument, and the NeetCode problems.

Coding Interview

Jason Yang · 03 Aug, 2026

Dynamic programming in Java without the fear: how to name the state and find the recurrence, the 1D DP problem families, and when to memoize vs tabulate.

Coding Interview

Jason Yang · 03 Aug, 2026

Binary search in Java, beyond the sorted-array lookup: the boundary template that kills off-by-one bugs, searching on the answer, and rotated-array problems.

Coding Interview

Jason Yang · 03 Aug, 2026

The sliding-window pattern in Java: fixed vs variable windows, what to track inside, and how it solves Longest Substring and Minimum Window in one O(n) pass.

AI & LLM

Jason Yang · 22 Jul, 2026

The hard part of a Claude Code agent loop isn't repeating work. It's a stop condition you can trust: convergent vs exploratory, and who enforces the verdict.

AI & LLM

Jason Yang · 22 Jul, 2026

Claude Code's /goal decides it's done from the worker's self-report. Add a Stop hook that verifies completion with exit codes, not the model's word.

AI & LLM

Jason Yang · 22 Jul, 2026

Karpathy's autoresearch pattern rebuilt for Claude Code: a Bash loop that scores each AI-tried hypothesis, keeps improvements, and rolls back failures with git.

Tools

Jason Yang · 19 Jul, 2026

Imgur's OAuth flow stopped working, so I moved my Obsidian attachments local: the /assets + UUID setup, the migration, and the settings that cost me an evening.

AI & LLM

Jason Yang · 12 Jul, 2026

Three Claude Code skills for downloading YouTube captions as SRT, transcribing audio with a local Whisper server, and translating embedded subtitle tracks.

AI & LLM

Jason Yang · 09 Jul, 2026

What an AI harness is and how to build one — validation, gates, and Generator ≠ Evaluator separation at each stage of the SDLC.

AI & LLM

Jason Yang · 08 Jul, 2026

AI engineering is more than prompts. A practical frame — prompt, context, harness, loop — walked through one example: an AI that reviews every PR.

Tools

Jason Yang · 05 Jul, 2026

Widen the Obsidian Nord editor with a CSS snippet, and keep Korean aligned by stacking JetBrains Mono with D2Coding. No theme edits, just a snippet and a few fonts.

Tools

Jason Yang · 05 Jul, 2026

Ghostty 1.3 lets you pin a tab's title so Claude Code and Codex tabs stop renaming themselves — set it with the prompt_tab_title keybind action.

Homelab

Jason Yang · 04 Jul, 2026

Move a self-hosted Ghost blog on Synology NAS from port forwarding to a Cloudflare Tunnel: no open inbound ports, home IP hidden, ads.txt via a free Worker.

AI & LLM

Jason Yang · 02 Jul, 2026

Screenshots won't paste into Claude Code on Wayland? Install wl-clipboard (not xclip), then restart the CLI. Same fix works for Codex.

Homelab

Jason Yang · 14 Jun, 2026

Bitwarden extension can't log into your self-hosted Vaultwarden? Update the Docker image on Synology NAS to fix the compatibility error.

AI & LLM

Jason Yang · 09 Jun, 2026

Run the Ralph Loop in Claude Code: four ways to repeat work and stop on clear completion criteria — the ralph-loop plugin, /loop, a prompt loop, and Bash.

AI & LLM

Jason Yang · 05 Jun, 2026

The Claude Code debate over Markdown vs HTML for AI output — and why the real issue isn't the format but how clearly AI communicates structure and intent.

Framework

Jason Yang · 02 Jun, 2026

Optimistic locking in Spring Boot and JPA: how it works and how to make it production-ready with retries, backoff, jitter, observability, and fallback.

AI & LLM

Jason Yang · 23 May, 2026

Zed's Terminal Threads run Claude Code, Codex, and other CLI AI agents right inside the editor — a lightweight AI workflow without moving to VS Code or Cursor.

Linux

Jason Yang · 20 May, 2026

Ghostty split panes on Linux: default shortcuts, pane navigation, resizing, zoom mode, and custom keybindings.

System Design

Jason Yang · 13 May, 2026

The Liskov Substitution Principle in Java: why the classic Rectangle/Square example violates LSP, and how smaller interfaces or composition fix the design.

System Design

Jason Yang · 13 May, 2026

Apply the Open-Closed Principle in Java with the Strategy Pattern — add new behavior without editing core logic, shown with a payment-processing example.

System Design

Jason Yang · 13 May, 2026

DIP vs DI in Java: they work together but differ — DIP keeps logic depending on abstractions, DI supplies dependencies from outside. Explained with examples.

System Design

Jason Yang · 12 May, 2026

SOLID principles in Java explained with simple examples — SRP, OCP, LSP, ISP, and DIP, each with backend-focused code. The full series index starts here.

System Design

Jason Yang · 12 May, 2026

Dependency Inversion Principle in Java, explained with notification, payment gateway, Spring Boot, and testing examples.

System Design

Jason Yang · 12 May, 2026

The Interface Segregation Principle in Java: why one fat interface forces empty methods and UnsupportedOperationException, and how small focused interfaces fix it — with phone, printer, and backend examples.

System Design

Jason Yang · 12 May, 2026

The Liskov Substitution Principle in Java: why a subclass that breaks its parent's contract violates LSP, shown with bird, Flyable, and discount policy examples.

System Design

Jason Yang · 12 May, 2026

The Open-Closed Principle in Java: add new behavior without touching stable code, shown with payment methods, interfaces, and Spring Boot style examples.

System Design

Jason Yang · 12 May, 2026

The Single Responsibility Principle in Java: what 'one reason to change' actually means in practice, with backend service and Spring Boot style examples.

AI & LLM

Jason Yang · 03 May, 2026

opusplan, subagents, and /advisor all pick models in Claude Code but fire on different signals — here's what each does and why you'd run all three.

Linux

Jason Yang · 26 Apr, 2026

Wine and Bottles can't reliably run KakaoTalk anymore thanks to Themida. Here's how I got it working on Ubuntu 25.10 using Waydroid instead.

System Design

Jason Yang · 26 Apr, 2026

Fuzzy search in PostgreSQL with pg_trgm: the operators, the GIN vs GiST index decision, and the tuning that keeps autocomplete from breaking in production.

Linux

Jason Yang · 24 Apr, 2026

Kate's Markdown preview shows up blank on Kubuntu 25.10? The plugin is fine — it's just missing a tiny KPart package. One-line fix inside.

Linux

Jason Yang · 21 Apr, 2026

Chrome silent on Kubuntu while Firefox plays fine? A three-line PipeWire state reset clears stale routing and fixes it.

Tools

Jason Yang · 20 Apr, 2026

tmux keeps your sessions alive through dropped SSH connections and closed terminals. Here’s how to install and set it up on Ubuntu/Kubuntu, plus a Ghostty workflow.

Linux

Jason Yang · 18 Apr, 2026

Dolphin as your default file manager on Ubuntu 24.04: install steps, the pitfalls that break file dialogs, and what still depends on Nautilus.

AI & LLM

Jason Yang · 16 Apr, 2026

Claude Code’s /statusline shows the project, model, and git branch right in your terminal — so you never lose track of which AI session is in which tab.

AI & LLM

Jason Yang · 12 Apr, 2026

Pair Claude Code with Codex in one workflow: how I set it up, and why using one model to generate code and another to review it leads to better results.

Coding Interview

Jason Yang · 31 Mar, 2026

Minimum Window Substring (LeetCode 76): the sliding-window O(n) approach with character counts to shrink to the smallest valid window, with a visual.

Coding Interview

Jason Yang · 31 Mar, 2026

Longest Substring Without Repeating Characters (LeetCode 3): the sliding-window O(n) approach, and why the int[128] version can jump the left pointer instead of stepping — with interactive visuals.

Coding Interview

Jason Yang · 31 Mar, 2026

Valid Palindrome (LeetCode 125): the two-pointer O(n) check that skips non-alphanumerics in place, why it beats building a cleaned string, and the edge cases.

Coding Interview

Jason Yang · 30 Mar, 2026

Longest Consecutive Sequence (LeetCode 128): the hash-set O(n) trick that only counts from sequence starts, with an interactive step-by-step visual.

Tools

Jason Yang · 30 Mar, 2026

Migrate from SecureCRT to Ghostty: SSH config, key-based auth, and shell scripts for a developer-friendly SSH workflow with clean log management.

Cloud & DevOps

Jason Yang · 29 Mar, 2026

Struggling with CORS errors in GCP? How CORS actually works across GCS, API Gateway, and Signed URLs, with practical examples and debugging tips.

Coding Interview

Jason Yang · 27 Mar, 2026

3Sum (LeetCode 15): sort then two-pointer for an O(n^2) solution, why sorting unlocks it, and the three places duplicate triplets sneak in — with an interactive visualization.

Coding Interview

Jason Yang · 27 Mar, 2026

Container With Most Water (LeetCode 11): the two-pointer O(n) approach, and the short proof for why moving the shorter line never skips a better answer — with an interactive visualization.

Coding Interview

Jason Yang · 27 Mar, 2026

The two-pointer pattern in Java: how converging pointers turn an O(n²) brute force into a single O(n) pass, and the decision rule that makes it safe.

System Design

Jason Yang · 26 Mar, 2026

A practical Kafka testing strategy using Spring EmbeddedKafka and Python testcontainers. Learn how to test producers and consumers with real Kafka instead of mocks.

System Design

Jason Yang · 26 Mar, 2026

Implement a Kafka consumer in FastAPI with aiokafka: async processing, manual offset commit, error handling, and idempotency patterns for production.

System Design

Jason Yang · 26 Mar, 2026

Implement a Kafka producer in FastAPI with aiokafka (async-first): pydantic-settings, event schema design, lifecycle management, and production best practices.

System Design

Jason Yang · 26 Mar, 2026

Implement a Kafka producer and consumer in Spring Boot: KafkaTemplate, @KafkaListener, manual ACK, retry handling, and Dead Letter Topic best practices.

System Design

Jason Yang · 26 Mar, 2026

Set up Kafka locally with Docker Compose and design scalable topic naming: partition keys, debugging, and real-world best practices in one practical guide.

System Design

Jason Yang · 26 Mar, 2026

Kafka essentials for beginners: topics, partitions, consumer groups, and ACKs explained in a practical, easy-to-understand way — core concepts made simple.

Cloud & DevOps

Jason Yang · 25 Mar, 2026

Set up HTTPS with Certbot, Let's Encrypt, and Nginx in Docker: certificate issuance, renewal, and full automation in a simple, practical walkthrough.

Cloud & DevOps

Jason Yang · 25 Mar, 2026

Set up a local Docker registry on your LAN to build and deploy images across machines with no cloud costs — plus automated redeploys with Watchtower, all free.

Programming Language

Jason Yang · 22 Mar, 2026

When to use HashSet, LinkedHashSet, or TreeSet in Java: their differences explained simply, and how they map to Python's set, dict, and sorted().

Linux

Jason Yang · 11 Feb, 2026

Set up a Caddy reverse proxy with automatic HTTPS using Docker: configure port forwarding, Docker Compose, and automatic certificate renewal.

Troubleshooting

Jason Yang · 08 Feb, 2026

Log in to the TELUS Network Access Hub (NAH) at 192.168.1.254 to set up DDNS and port forwarding — how to tell the NAH from the Wi-Fi Hub and find its IP.

Framework

Jason Yang · 26 Jan, 2026

MapStruct is a compile-time mapping tool for Spring projects that reduces boilerplate, improves safety, and makes DTO mapping cleaner and more testable.

Framework

Jason Yang · 23 Jan, 2026

Pydantic v2 settings give you type-safe, environment-driven config. Covers default, default_factory, and FastAPI integration best practices.

Programming Language

Jason Yang · 08 Jan, 2026

FastAPI vs Spring Core: how Python and Java differ on DI, singleton scope, resource lifecycle, and execution models — a practical developer comparison.

Programming Language

Jason Yang · 08 Jan, 2026

FastAPI dependency injection is a request-scoped resource engine, not just object passing. Covers lifecycles, dependency chains, testing, and clean architecture.

Programming Language

Jason Yang · 08 Jan, 2026

The Python Singleton pattern ensures one instance per process. Here are the Pythonic ways to do it (module-level, decorator, metaclass), plus thread safety and when not to use it.

Homelab

Jason Yang · 05 Jan, 2026

Set up SSH key-based login from Ubuntu to a Synology NAS (DSM 7.1) for secure, passwordless access — enable User Home, add your key, and disable password auth.

AI & LLM

Jason Yang · 05 Jan, 2026

Claude Code Subagents get their power from Skills. Combine reusable expertise with independent execution to build smarter automated workflows.

AI & LLM

Jason Yang · 04 Jan, 2026

Claude Code Skills package repeatable workflows so Claude automates code reviews, enforces project conventions, and keeps quality consistent across a team.

AI & LLM

Jason Yang · 04 Jan, 2026

AI code generation breaks architecture without guardrails. Learn how .claude/rules enforce consistent FastAPI layers with practical, team-driven constraints.

AI & LLM

Jason Yang · 04 Jan, 2026

Install the NVIDIA 535 driver on Ubuntu 24.04 and fix the dependency conflicts (pkgProblemResolver breaks) — clean purge, right driver, then verify PyTorch CUDA.

Homelab

Jason Yang · 04 Jan, 2026

Automate Ghost blog feature-image optimization with a Bash + ImageMagick script that trims, centers, and converts to 16:9 WebP for faster LCP.

AI & LLM

Jason Yang · 03 Jan, 2026

Generate speaker-labeled subtitles on Ubuntu 24.04 with Whisper and pyannote.audio (CUDA GPU) — a full working setup from Python 3.10 to a combined transcript + speaker SRT.

Programming Language

Jason Yang · 01 Jan, 2026

Lombok's @Builder ignores your field defaults — use @Builder.Default or final to keep them. Here's why it happens and how to fix it.

Homelab

Jason Yang · 01 Jan, 2026

Docmost on Synology NAS with Docker, step by step — including the reverse proxy + WebSocket setup that fixes the 'Real-time editor connection lost' error.

Tools

Jason Yang · 01 Jan, 2026

Format JSON in Vim on Ubuntu with jq — install it, then prettify or minify a buffer with a single `:%!jq` filter, or straight from the command line.

Homelab

Jason Yang · 01 Jan, 2026

Vaultwarden (Bitwarden) on Synology NAS with Docker: a secure, lightweight, free LastPass alternative with HTTPS. Here's the full setup.

AI & LLM

Jason Yang · 29 Dec, 2025

Use DeepSeek-Reasoner directly with Claude Code CLI via its Anthropic-compatible endpoint — no local proxy or router. Set a few env vars and switch models.

AI & LLM

Jason Yang · 28 Dec, 2025

Claude Code can add Co-authored-by metadata to your commits, causing Claude to appear in GitHub Contributors. Here’s why it happens and how to disable it.

AI & LLM

Jason Yang · 26 Dec, 2025

Claude Code forgets everything when a session ends. Install claude-mem to persist context, fix common issues, and enable long-term memory for real workflows.

System Design

Jason Yang · 20 Dec, 2025

PostgreSQL TIMESTAMP WITH TIME ZONE (timestamptz) normalizes everything to UTC and prevents timezone bugs that only surface in production. Here's why it should be your default and how to migrate safely.

System Design

Jason Yang · 16 Dec, 2025

Secure PostgreSQL by separating admin and app roles: SQL scripts for schema hardening and automated permissions, for Cloud SQL, AWS RDS, or self-hosted.

Cloud & DevOps

Jason Yang · 07 Dec, 2025

GCP Service Account Impersonation lets your MFA-authenticated account borrow a service account's permissions with short-lived tokens instead of risky key.json files. Here's the 3-step setup.

AI & LLM

Jason Yang · 06 Dec, 2025

Ubuntu desktop crashing under heavy dev workloads? You're likely hitting the OOM killer. The exact swap and swappiness setup that stops the crashes.

Linux

Jason Yang · 05 Dec, 2025

Still using grep? Meet ripgrep (rg), the ultra-fast Rust search tool that respects .gitignore by default and searches your codebase in seconds.

Linux

Jason Yang · 05 Dec, 2025

Run an Ubuntu laptop in clamshell mode — lid closed on an external monitor — while it still sleeps normally in your bag. The conditional HandleLidSwitchDocked fix, plus the display and input setup.

Linux

Jason Yang · 05 Dec, 2025

Install and configure OpenSSH Server on Ubuntu: the install steps, UFW firewall setup, and connection testing for Ubuntu 22.04, 24.04, and newer.

Linux

Jason Yang · 04 Dec, 2025

Fix "Address already in use" errors on Ubuntu/Linux. Quickly identify port-hogging processes with ss, lsof, or netstat and terminate them safely.

Cloud & DevOps

Jason Yang · 04 Dec, 2025

TCP explained: how the segment header, the 3-way handshake, and flow control build a reliable connection over an unreliable network.

Linux

Jason Yang · 04 Dec, 2025

SSH lag on Ubuntu? Your Wi-Fi card may be entering sleep mode. Disable Wi-Fi power management to keep the connection responsive — quick step-by-step.

Linux

Jason Yang · 03 Dec, 2025

Need a static WiFi IP on Ubuntu without router access? Learn how to use nmcli for laptops (GUI-safe) or Netplan for servers to set a fixed IP.

Coding Interview

Jason Yang · 03 Dec, 2025

Search in Rotated Sorted Array (LeetCode 33): a modified O(log n) binary search that finds which half is sorted, with an interactive step visual.

Linux

Jason Yang · 03 Dec, 2025

Safely open a specific port on Ubuntu with UFW: check status, enable the firewall without losing SSH access, and verify your rules — step by step.

Tools

Jason Yang · 03 Dec, 2025

Back up and restore your full SecureCRT configuration on Ubuntu with simple terminal commands so you never lose saved sessions when migrating or reinstalling.

Coding Interview

Jason Yang · 03 Dec, 2025

Divide and Conquer is more than Merge Sort: the 3-step design paradigm, how it differs from plain recursion, and the interview patterns that use it.

Homelab

Jason Yang · 02 Dec, 2025

Enable SSH on Synology NAS and log in as root using 'sudo -i'. A quick guide for advanced DSM administration and secure terminal access.

Tools

Jason Yang · 02 Dec, 2025

Set up a serial console connection in SecureCRT to HP servers (DL380/DL580, HP-UX) — the exact baud rate, data bits, parity, and flow-control settings.

Coding Interview

Jason Yang · 02 Dec, 2025

Binary Search runs in O(log n) because it halves the search space every step. Here's the intuition, the math proof, and how it compares to linear search.

Coding Interview

Jason Yang · 02 Dec, 2025

Find Minimum in Rotated Sorted Array (LeetCode 153): the O(log n) binary search that locates the rotation pivot, explained step by step with examples.

Programming Language

Jason Yang · 02 Dec, 2025

Add a gRPC endpoint to a Spring Boot order-service: define .proto files, generate stubs, implement the RPC logic, and expose a new CreateOrder API.

Coding Interview

Jason Yang · 01 Dec, 2025

Dynamic Programming demystified: at its core, DP is just Divide and Conquer plus memory. See the connection and it gets far easier to explain in interviews.

Coding Interview

Jason Yang · 01 Dec, 2025

Maximum Product Subarray (LeetCode 152): why you track max and min together to handle negatives and zeros, and the O(n) dynamic-programming solution.

Tools

Jason Yang · 01 Dec, 2025

Easily download YouTube videos as high-quality MP3s on Ubuntu. Use yt-dlp and FFmpeg to convert audio and embed thumbnails with simple commands.

Tools

Jason Yang · 01 Dec, 2025

Batch trim MP3s on Ubuntu with FFmpeg. Use this simple shell script to cut audio files instantly without re-encoding or quality loss.

Tools

Jason Yang · 01 Dec, 2025

Easily merge two mono audio files into a single stereo track using FFmpeg on Ubuntu. Perfect for syncing dual-mic interviews and podcasts.

Tools

Jason Yang · 01 Dec, 2025

Batch convert video (MKV, MP4, AVI) to MP3 on Ubuntu with a simple FFmpeg shell script — no manual re-encoding, run it once on a whole folder.

Tools

Jason Yang · 01 Dec, 2025

Convert WAV or MP4 audio to MP3 with FFmpeg — the exact command-line options for input, bitrate, and quality, with examples you can copy and run.

Tools

Jason Yang · 01 Dec, 2025

Fix the SecureCRT "Key exchange failed" error on Ubuntu 22.04. Learn how to enable compatible algorithms like curve25519-sha256 for a successful connection.

Programming Language

Jason Yang · 30 Nov, 2025

Pydantic vs dataclass: use Pydantic to validate incoming data, dataclasses for internal structures. Real examples and where each one breaks.

Cloud & DevOps

Jason Yang · 29 Nov, 2025

The OSI 7-layer model reference: each layer's function, protocols (HTTP, TCP/IP), PDUs, and devices in one table — great for CCNA and CompTIA prep.

Troubleshooting

Jason Yang · 29 Nov, 2025

Fix the ACPI BIOS Error when installing Ubuntu 22.04 on an ASUS GA502GU: bypass the install freeze with GRUB parameters and repair the bootloader after.

Coding Interview

Jason Yang · 29 Nov, 2025

Maximum Subarray (LeetCode 53): Kadane's algorithm explained as one decision — extend or restart — plus the O(n) to O(1) space drop and a full worked trace.

Programming Language

Jason Yang · 29 Nov, 2025

Exception logging in Java done right: catch errors in the correct layer, log them once, and keep clear context — practical patterns for real systems.

Programming Language

Jason Yang · 29 Nov, 2025

Design effective custom exceptions in Java: structure them well, separate business and system errors, and integrate cleanly with Spring Boot error handling.

Programming Language

Jason Yang · 28 Nov, 2025

Why real Spring Boot developers prefer unchecked exceptions over the textbook rules — modern exception-handling patterns for clean, maintainable service code.

Coding Interview

Jason Yang · 28 Nov, 2025

Product of Array Except Self (LeetCode 238): the prefix and suffix product trick that avoids division for an O(n) solution, with an interactive visual.

Coding Interview

Jason Yang · 28 Nov, 2025

Prefix Sum and Suffix Product explained: what these algorithm terms really mean, why they beat naive recomputation, and where they show up in problems.

Coding Interview

Jason Yang · 27 Nov, 2025

Contains Duplicate (LeetCode 217): compare the brute-force, sorting, and hash-set approaches — and why 'just use a hash set' isn't always the right reflex.

Programming Language

Jason Yang · 27 Nov, 2025

Understand Java's Throwable hierarchy — Error vs Exception, checked vs unchecked, and RuntimeException — to write safer error handling in production apps.

Coding Interview

Jason Yang · 27 Nov, 2025

One-pass and greedy algorithms: how a single scan and greedy choices process large data with minimal memory — the core ideas and when they're optimal.

Coding Interview

Jason Yang · 26 Nov, 2025

Best Time to Buy and Sell Stock (LeetCode 121): the single-pass O(n) solution that tracks the lowest price so far, with an interactive step-by-step visual.

Linux

Jason Yang · 26 Nov, 2025

Set up Vim with vim-plug on Ubuntu step by step: create the required directories, configure your .vimrc for a better coding setup, and install plugins.

Tools

Jason Yang · 26 Nov, 2025

Install SecureCRT on Ubuntu 24.04 LTS and fix the libxcb-cursor0 dependency error — the .deb steps plus the one command that resolves it.

Tools

Jason Yang · 26 Nov, 2025

Automate SecureCRT logins to a PostgreSQL database over SSH with a Python Logon Actions script — full setup, the script itself, and jump-server tips.

Cloud & DevOps

Jason Yang · 25 Nov, 2025

Publish private Python libraries to GCP Artifact Registry with Poetry: the critical publish-vs-install URL distinction that avoids 404s, plus auth tokens.

Homelab

Jason Yang · 24 Nov, 2025

Add math rendering to Ghost with KaTeX: lightweight LaTeX support via Code Injection to display algorithm complexity like O(n) and equations beautifully.

Linux

Jason Yang · 22 Nov, 2025

Run an old Ubuntu laptop as a 24/7 headless server with the lid closed: stop it sleeping from the lid, idle timeout, and every sleep target — the logind.conf fix plus systemctl mask (20.04/22.04/24.04).

Framework

Jason Yang · 22 Nov, 2025

Spring Boot 'required a bean of type String' error? It often hits when switching to constructor injection. How to correctly inject @Value into constructors.

Homelab

Jason Yang · 22 Nov, 2025

Blocked from updating BIOS due to low battery? Here is a workaround to bypass the restriction on ASUS laptops using the F11 trick.

System Design

Jason Yang · 22 Nov, 2025

Rate Limiting vs Throttling: often used interchangeably but different — rate limiting controls user quotas, throttling protects system health. The key differences.

Cloud & DevOps

Jason Yang · 22 Nov, 2025

Change the hostname on Amazon Linux so it survives a reboot — edit /etc/sysconfig/network, /etc/hostname, and /etc/hosts so the change persists.

Framework

Jason Yang · 22 Nov, 2025

Integrate Swagger (OpenAPI) into Spring Boot with springdoc: secure your endpoints with JWT auth and auto-generate the API docs.

Cloud & DevOps

Jason Yang · 18 Nov, 2025

Connect to GCP Cloud SQL (PostgreSQL) from your local machine with Cloud SQL Auth Proxy — an IAM-authenticated TLS tunnel, no public IP or static passwords.

System Design

Jason Yang · 17 Nov, 2025

Reliability vs availability: reliability is how long a system runs without failing; availability is how much of the time it's up. Examples and how to raise each.

Programming Language

Jason Yang · 17 Nov, 2025

Manage FastAPI projects with Poetry: project setup, dependency locking, virtual environments, and testing — the full pyproject.toml workflow for teams.

Programming Language

Jason Yang · 17 Nov, 2025

Migrating Pydantic v1 to v2 in a FastAPI project? Here's the full v1→v2 checklist plus the validator, settings, and config changes that break.

Programming Language

Jason Yang · 14 Nov, 2025

Checked exceptions are enforced by the Java compiler; unchecked ones aren't — here's the difference, with the class hierarchy, code examples, and when each applies.

Linux

Jason Yang · 14 Nov, 2025

Install the latest Vim 9.x on Ubuntu/Linux via PPA and turn the terminal into an IDE: plugin manager setup, a ready .vimrc, and essential plugins.

Linux

Jason Yang · 13 Nov, 2025

Set an SSH login banner on Ubuntu 24.04 to warn unauthorized users and hide OS version info — configure /etc/issue.net and sshd_config the right way.

Linux

Jason Yang · 13 Nov, 2025

Remove ^M (carriage return) characters from text files on Linux/Unix after transfer from Windows — fixes with dos2unix, sed, tr, and Vim, how to verify, and why they appear.

Linux

Jason Yang · 12 Nov, 2025

Set Terminator as the default terminal on Ubuntu. This step-by-step developer guide covers installation, setup, and integration with VS Code.

Linux

Jason Yang · 12 Nov, 2025

Does your set guifont in .vimrc work on Windows but break on Ubuntu? Learn the critical syntax difference (colons vs. backslashes) for gVim fonts.

Linux

Jason Yang · 12 Nov, 2025

Install and manage a WireGuard VPN client on Ubuntu: set it up, connect with wg-quick up, verify the status, and safely disconnect.

Linux

Jason Yang · 12 Nov, 2025

Bulk-rename files in Linux with the rename command and Perl regex: normalize whitespace, strip unwanted metadata, and batch-rename in one quick command.

Coding Interview

Jason Yang · 11 Nov, 2025

Two Sum (LeetCode 1) two ways: the brute-force O(n^2) scan vs the hash-map O(n) approach — with the intuition, edge cases, and the space-time trade-off.

Linux

Jason Yang · 11 Nov, 2025

Fix Vim keeping your IME active in Normal mode (stray Korean/Japanese on j or dd): set up vim-im-select with ibus for automatic, seamless IME switching.

Linux

Jason Yang · 10 Nov, 2025

Chrome breaking Bluetooth audio on Ubuntu 24? Permanently fix the stutter by locking your device to the high-fidelity A2DP profile with pavucontrol.

Framework

Jason Yang · 05 Nov, 2025

React Query (TanStack Query) manages server state: smart query-key design, useQuery caching, and the 3-step optimistic update flow.