docs: add comprehensive algorithms guide

- Add ALGORITHMS.md guide for algorithm and data structure preparation
- Include overview of all core algorithm topics
- Document structure and usage guide
- List related system design topics
- Provide getting started instructions

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

ALGORITHMS.md

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+# Algorithm and Data Structure Interview Guide
+
+## Overview
+
+This repository contains comprehensive algorithm and data structure interview questions with detailed explanations, implementations, and practical applications.
+
+## Core Algorithm Topics
+
+### 1. B+ Tree (B+ 树)
+- **Location**: `questions/alg-btree.md`
+- **Focus**: Database indexing, file systems
+- **Key Features**: Multi-way search tree, ordered leaves, efficient range queries
+- **Applications**: MySQL, PostgreSQL, file systems
+
+### 2. LRU Cache (LRU 缓存)
+- **Location**: `questions/alg-lru.md`
+- **Focus**: Cache eviction strategies
+- **Key Features**: Least Recently Used eviction, O(1) operations
+- **Applications**: Web caching, database query caching, memory management
+
+### 3. Red-Black Tree (红黑树)
+- **Location**: `questions/alg-redblacktree.md`
+- **Focus**: Self-balancing binary search tree
+- **Key Features**: Red/black coloring, O(log n) operations
+- **Applications**: Java TreeMap, Linux kernel, database indexes
+
+### 4. Skip List (跳表)
+- **Location**: `questions/alg-skip-list.md`
+- **Focus**: Probabilistic data structure
+- **Key Features**: Multi-level linked list, O(log n) operations
+- **Applications**: Redis sorted sets, database indexes, routing tables
+
+### 5. Timing Wheel (时间轮)
+- **Location**: `questions/alg-timingwheel.md`
+- **Focus**: Task scheduling and delayed execution
+- **Key Features**: Hierarchical time buckets, efficient task management
+- **Applications**: Distributed systems, message queues, cache expiration
+
+## Documentation Structure
+
+Each algorithm document includes:
+
+### Core Components
+1. **原理 (Principle)**: Detailed explanation of the data structure
+2. **图解说明 (Visual Explanation)**: Diagrams and examples
+3. **Java 代码实现 (Java Implementation)**: Complete working code
+4. **时间复杂度分析 (Time Complexity)**: Performance analysis
+5. **实际应用场景 (Practical Applications)**: Real-world use cases
+6. **与其他数据结构的对比 (Comparison)**: With other data structures
+
+### Interview Focus Areas
+- **Time Complexity**: Big O analysis for all operations
+- **Space Complexity**: Memory usage analysis
+- **Practical Applications**: Where and why to use each structure
+- **Common Interview Questions**: Q&A sections with detailed answers
+
+## Usage Guide
+
+### For Interview Preparation
+1. Start with **B+ Tree** - fundamental for database understanding
+2. Study **LRU Cache** - essential for system design interviews
+3. Learn **Red-Black Tree** - important for understanding balanced trees
+4. Explore **Skip List** - shows probabilistic approaches to balancing
+5. Master **Timing Wheel** - crucial for distributed systems
+
+### For Practical Implementation
+- Each document includes multiple implementation approaches
+- Start with the basic implementation, then explore advanced variants
+- Study the concurrent implementations for production use
+- Understand the trade-offs between different approaches
+
+### Key Learning Points
+1. **Understand the "Why"**: Not just how, but why each structure exists
+2. **Trade-offs**: Every structure has pros and cons - understand them
+3. **Performance**: Always consider time and space complexity
+4. **Practical Use**: Match the right structure to the right problem
+
+## Additional Resources
+
+### System Design Topics
+- `questions/database-sharding.md`: Database sharding strategies
+- `questions/message-queue.md`: Message queue implementations
+- `questions/rate-limiting.md`: Rate limiting algorithms
+- `questions/consistency-hash.md`: Consistent hashing
+
+### Performance Optimization
+- `questions/mysql-index-optimization.md`: MySQL index optimization
+- `questions/replication-delay.md`: Database replication strategies
+- `questions/cache-problems.md`: Cache problems and solutions
+
+### Microservices and Distributed Systems
+- `questions/distributed-id.md`: Distributed ID generation
+- `questions/distributed-transaction.md`: Distributed transactions
+- `questions/design-feed.md`: Feed system design
+- `questions/design-lbs.md`: Load balancing systems
+- `questions/design-seckill.md`: Flash sale system design
+- `questions/design-shorturl.md`: Short URL system design
+- `questions/design-im.md`: Instant messaging system design
+
+## Getting Started
+
+1. **Read through each document** to understand the fundamentals
+2. **Run the code examples** to see implementations in action
+3. **Practice the interview questions** at the end of each document
+4. **Compare different approaches** to understand trade-offs
+5. **Implement your own versions** to solidify understanding
+
+## Contributing
+
+This is a living document. Feel free to:
+- Add new algorithm topics
+- Improve existing explanations
+- Add more code examples
+- Enhance the Q&A sections
+- Share real-world use cases
+
+## License
+
+This project is open source and available under the MIT License.
+
+---
+
+**Note**: All documents are written in Chinese for clarity and accessibility. The code examples are in Java for widespread understanding.