📚 A-Level Edexcel Computer Science: Last-Minute Revision Notes | A-Level Edexcel 计算机科学：考前冲刺笔记
This last-minute revision guide provides a concise overview of the core topics for the Edexcel A-Level Computer Science specification, helping you focus on key concepts, common algorithms, and essential theory before the exam.
本考前冲刺指南精简概述了Edexcel A-Level计算机科学考试大纲的核心主题，帮助你在考前聚焦关键概念、常见算法与必要理论。
1. Thinking Abstractly and Procedurally | 抽象思维与过程化思维
Abstraction involves removing irrelevant details to create a simplified model. In computer science, this helps manage complexity at different levels, from high-level design to low-level implementation.
抽象涉及去除无关细节以创建简化模型。在计算机科学中，这有助于在不同层次管理复杂度，从高层设计到低层实现。
Procedural abstraction (stepwise refinement) breaks a solution down into reusable procedures, each with a clear interface. Top-down design and structured diagrams support this approach.
过程化抽象（逐步求精）将解决方案分解为可重用的过程，每个过程具有清晰的接口。自顶向下设计和结构图支持这种方法。
Data abstraction hides the implementation details of data structures, allowing programmers to use them via defined operations. For example, a stack provides push and pop without revealing its internal array or linked list.
数据抽象隐藏了数据结构的实现细节，允许程序员通过定义的操作来使用它们。例如，栈提供 push 和 pop 而不暴露其内部数组或链表。
2. Data Representation and Structures | 数据表示与数据结构
Positive integers are stored in binary; signed integers typically use two's complement to represent negative values, where the most significant bit (MSB) is the sign bit.
正整数以二进制存储；有符号整数通常使用补码表示负值，其中最高有效位(MSB)是符号位。
recision and range determined by mantissa and exponent bit lengths. Rounding errors can occur.
浮点数遵循格式 ± 尾数 × 2^指数，其精度和范围由尾数和指数的位长决定。可能出现舍入误差。
Character encoding schemes like ASCII (7-bit) and Unicode (variable-length) map characters to numeric codes. Unicode supports global scripts and emojis.
像ASCII（7位）和Unicode（变长）等字符编码方案将字符映射到数字代码。Unicode支持全球文字和表情符号。
Key data structures: arrays (fixed size, direct access), records (heterogeneous fields), stacks (LIFO), queues (FIFO), linked lists (dynamic, efficient insertion/deletion), graphs (nodes and edges) and trees (hierarchical, binary search trees).
关键数据结构：数组（固定大小，直接访问），记录（异构字段），
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