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+@CLAUDE.md
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+# CLAUDE.md
+
+This file provides guidance to AI coding assistants (Claude Code, Cursor, OpenCode, etc.) when working with code in this repository.
+
+## Repository Overview
+
+This is [doocs/leetcode](https://github.com/doocs/leetcode) — a large collection of LeetCode, Coding Interviews, and other algorithm problem solutions, each implemented in multiple programming languages (Python, Java, C++, Go, TypeScript, Rust, C#, PHP, JavaScript, Kotlin, Swift, Scala, Ruby, Nim, Shell, SQL).
+
+## Directory Structure
+
+- **`solution/`** — Main LeetCode solutions, organized by problem number ranges (e.g., `0000-0099/`, `0100-0199/`). Each problem has its own directory (e.g., `0000-0099/0001.Two Sum/`) containing:
+    - `README.md` / `README_EN.md` — Chinese/English problem descriptions
+    - `Solution.{py,java,cpp,go,ts,cs,rs,...}` — Solution files in each language
+    - Follow standard LeetCode class-based structure: `class Solution` with the method
+
+- **`lcof/`** — 剑指 Offer (Coding Interviews, 2nd Edition) — problem directories named with Chinese titles
+- **`lcof2/`** — 剑指 Offer 专项突击版 (Coding Interviews, Special Edition)
+- **`lcci/`** — 程序员面试金典 (Cracking the Coding Interview, 6th Edition) — `01.01.Is Unique` format
+- **`lcp/`** — LeetCode Contest Problems
+- **`lcs/`** — LeetCode Contest (separate series)
+- **`basic/`** — Basic algorithm implementations (sorting algorithms like BubbleSort, QuickSort, etc.)
+
+## Development Workflow
+
+### Adding a New Solution
+
+1. Create a new problem directory under the appropriate parent (e.g., `solution/0000-0099/0042.My Problem/`)
+2. Add `Solution.py`, `Solution.java`, `Solution.cpp`, `Solution.go`, `Solution.ts`, `Solution.rs`, `Solution.cs`, etc.
+3. Add `README.md` and `README_EN.md` with problem description and solution explanations
+4. Follow the existing templates in `solution/template.md` for README formatting
+5. All language solutions must implement the same algorithm logic
+
+### Code Formatting
+
+All code must be formatted before committing. The lint-staged hooks run automatically on pre-commit:
+
+```bash
+# JavaScript/TypeScript/PHP/SQL/Markdown
+npx prettier --write "**/*.{js,ts,php,sql,md}"
+
+# Python
+py -m black -S <file>
+
+# C/C++/Java
+npx clang-format -i --style=file <file>
+
+# Go
+gofmt -w <file>
+
+# Rust
+rustfmt <file>
+```
+
+Or run the full formatting script:
+
+```bash
+python run_format.py
+```
+
+### Installation
+
+```bash
+npm install        # Installs dev dependencies and triggers pip install for Python deps
+```
+
+### CI/CD
+
+GitHub Actions automatically run:
+
+- **clang-format** lint on C/C++/Java files
+- **Black** lint on Python files
+- **Prettier** on JS/TS/PHP/SQL/Markdown files
+- **Deploy** workflow for the documentation site
+
+## Solution Patterns
+
+- Python solutions use `List` from typing (imported implicitly by LeetCode environment)
+- Go solutions include `package main` header (added/removed by formatting script)
+- PHP solutions include `<?php` header (added/removed by formatting script)
+- SQL solutions uppercase built-in function names (handled by `run_format.py`)
+- C# solutions contributed by [@kfstorm](https://github.com/kfstorm)
+
+## Key Conventions
+
+- Problem directories follow naming convention: `{NUMBER}.{Problem Name with Spaces}`
+- Each solution file is named `Solution.{ext}` (capital S)
+- README files use special HTML comment markers for templating (e.g., `<!-- problem:start -->`, `<!-- solution:start -->`)
+- Solutions should match the problem's required class/method signature from LeetCode