https://xungirl.github.io/posts/Recent content in Posts on xun's BlogHugo -- 0.168.0enMon, 19 Oct 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-10-19-lc230-self-k-execution-order/Mon, 19 Oct 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-10-19-lc230-self-k-execution-order/用逐步图解看 LC 230 的 self.k 写法怎么执行：先一路向左钻到底，每个节点在自己的调用里减一次 k，以及找到答案后为什么还会「多减一次」。https://xungirl.github.io/posts/2026-10-12-backtracking/Mon, 12 Oct 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-10-12-backtracking/用三个可交互的逐步动画搞懂回溯：先用日常走迷宫看「前进—碰壁—后退」，再看 LC 78 子集的决策树（每个节点都是答案、start 不回头），最后看 LC 46 全排列（只有叶子是答案、used[] 剪枝）。中英双语。https://xungirl.github.io/posts/2026-10-12-subsets-start-loop/Mon, 12 Oct 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-10-12-subsets-start-loop/LC 78 子集画递归树时最容易错位的一点：每个节点都有「我的 start → 我的循环」和「循环里每个 i → 一个孩子」两件事，要分开看。附可逐步播放的动画、带缩进打印的验证代码和一张总表。中英双语。https://xungirl.github.io/posts/2026-10-10-tree-recursion-order/Sat, 10 Oct 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-10-10-tree-recursion-order/用可交互的逐步图解看清二叉树递归到底按什么顺序走：一路先钻到最左，左边返回后才去右边，两边都返回后才处理自己。以 LC 124 的 gain 函数为例。https://xungirl.github.io/posts/2026-10-09-lc230-kth-smallest-bst/Fri, 09 Oct 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-10-09-lc230-kth-smallest-bst/用可交互的逐步图解看懂 LC 230：BST 中序遍历为什么天然是升序、k 怎么一路倒数到 0，以及 k = 3 和 k = 4 时递归走向的唯一区别。https://xungirl.github.io/posts/2026-09-29-seattle-rainier/Tue, 29 Sep 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-09-29-seattle-rainier/Sep 30 – Oct 1 · 两天西雅图 + 雷尼尔雪山行程：拿车、接机、Post &amp; Pour、Mt. Rainier、湖边晚霞，和四家晚饭候选。https://xungirl.github.io/posts/2026-06-26-agent-permission-hooks/Fri, 26 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-06-26-agent-permission-hooks/手搓 coding agent 课程的第三、四节：怎么在工具执行前加三道权限闸门，怎么把这些检查抽象成 Hook 事件系统；附一个亲手绕过黑名单的实验，理解为什么字符串匹配是假安全。https://xungirl.github.io/posts/2026-06-26-agent-tool-use-dispatch/Fri, 26 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-06-26-agent-tool-use-dispatch/s02 Tool Use 学习笔记：从只有一个 bash，到给 agent 5 个专用工具。核心是 dispatch map（工具名→函数的派发表）和 safe_path 路径护栏，并用实验看清模型何时只调一个工具、何时一次调多个。https://xungirl.github.io/posts/2026-06-25-agent-loop-from-scratch/Thu, 25 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-06-25-agent-loop-from-scratch/从零手搓一个最小 agent loop：搞懂 agent 的本质（模型动嘴 + 代码动手 + loop 传话），并用两个亲手做的实验验证『append 就是 agent 的记忆』——鬼打墙实验和记忆对照实验。https://xungirl.github.io/posts/2026-06-15-fastapi-backend-for-agents/Mon, 15 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-06-15-fastapi-backend-for-agents/vibe coding 时代学 FastAPI 的进阶笔记：错误处理 HTTPException、文件上传、依赖注入 Depends、async/await 异步原理、数据库 SQLModel 与事务 ACID。每个知识点都标了「为什么 agent 要用」和「大厂面试怎么答」。https://xungirl.github.io/posts/2026-06-11-fastapi-basics/Thu, 11 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-06-11-fastapi-basics/从零上手 FastAPI 的一次完整记录：什么是后端接口、查询参数 vs 路径参数、用 Pydantic 接收请求体、装饰器路径怎么读、如何用 uvicorn 跑起来，以及怎么用 /docs 测试并读懂 200/422 状态码。https://xungirl.github.io/posts/2026-06-11-fastapi-response-model/Thu, 11 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/2026-06-11-fastapi-response-model/学 FastAPI 时整理的笔记：响应模型 response_model 怎么过滤敏感字段、请求体和查询参数到底怎么分、路由和函数参数各是什么意思。https://xungirl.github.io/posts/project-roadmap-timeline/Wed, 10 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/project-roadmap-timeline/I liked the progress timeline I built for TicketCoach&#39;s landing page so much that I turned it into a reusable Hugo shortcode — bright gradient for what&#39;s shipped, gray for what&#39;s next, and a line that grows as you scroll.https://xungirl.github.io/posts/rag-explained/Wed, 10 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/rag-explained/从白板笔记整理的 RAG 知识点：为什么需要 RAG、它的本质是什么、数据准备（chunking + embedding）和检索生成的完整流程。https://xungirl.github.io/posts/a-records-vs-cname-records/Tue, 09 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/a-records-vs-cname-records/What A records and CNAME records actually do, how they differ, and how I used them to connect a custom domain to a GitHub Pages site — including the gotchas that tripped me up.https://xungirl.github.io/posts/devlog-zh/Tue, 09 Jun 2026 00:00:00 +0000https://xungirl.github.io/posts/devlog-zh/按日期累积记录这个博客的每次改动，以及背后的前端原理。给自己留的学习笔记，以后每次改动继续往里加。https://xungirl.github.io/posts/blog-devlog/Wed, 06 May 2026 00:00:00 +0000https://xungirl.github.io/posts/blog-devlog/A running log of every meaningful change made to this blog — tech stack decisions, bug fixes, and feature additions.https://xungirl.github.io/posts/llm-agents-react/Fri, 01 May 2026 00:00:00 +0000https://xungirl.github.io/posts/llm-agents-react/A technical breakdown of LLM-based agents — the ReAct loop, tool calling, planning strategies, and the math behind why chain-of-thought helps.https://xungirl.github.io/posts/transformer-architecture/Mon, 20 Apr 2026 00:00:00 +0000https://xungirl.github.io/posts/transformer-architecture/A from-scratch walkthrough of the Transformer architecture — self-attention, multi-head attention, positional encoding, and why it replaced RNNs.https://xungirl.github.io/posts/my-first-post/Tue, 10 Feb 2026 00:00:00 +0000https://xungirl.github.io/posts/my-first-post/<h2 id="welcome">Welcome</h2> <p>Hi, I&rsquo;m Jiaju — a CS student at Northeastern University. This blog is where I share what I learn about programming, algorithms, and software engineering.</p> <h2 id="why-i-started-this-blog">Why I Started This Blog</h2> <p>Writing helps me think more clearly. By explaining concepts in my own words, I understand them better. Plus, it&rsquo;s a great way to track my learning journey.</p> <h2 id="a-quick-math-demo">A Quick Math Demo</h2> <p>The time complexity of merge sort can be expressed as:</p>