IB Computer Science: Last-Minute Revision Notes | IB 计算机：考前冲刺笔记

📚 IB Computer Science: Last-Minute Revision Notes | IB 计算机：考前冲刺笔记

This last-minute revision guide covers the essential topics for the IB Computer Science exam, including both SL and HL content. Use these concise notes to reinforce key concepts, definitions, and algorithms before the big day.

本考前冲刺指南涵盖了IB计算机科学考试的核心主题，包括标准水平（SL）和高级水平（HL）内容。用这些简明的笔记巩固关键概念、定义和算法，迎接考试。

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1. System Fundamentals | 系统基础

A system is an organized collection of parts that are integrated to accomplish an overall goal. Systems can be natural or man-made.

系统是一个有组织的部分集合，各部分整合以实现整体目标。系统可以是自然或人造的。

The systems life cycle includes: planning, analysis, design, implementation, testing, installation, and maintenance.

系统生命周期包括：规划、分析、设计、实施、测试、安装和维护。

Usability refers to how easy it is for users to interact with a system; accessibility ensures systems can be used by people with disabilities.

可用性是指用户与系统交互的容易程度；无障碍性确保残障人士也能使用系统。

Ethical considerations involve privacy, data security, intellectual property, and the digital divide. Green computing aims to reduce environmental impact through energy-efficient hardware and proper e-waste disposal.

伦理考量涉及隐私、数据安全、知识产权和数字鸿沟。绿色计算旨在通过节能硬件和妥善处理电子垃圾来减少对环境的影响。

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2. Computer Organization | 计算机组成

The CPU fetches, decodes, and executes instructions in a continuous cycle known as the fetch-decode-execute cycle.

CPU 在称为“取指-译码-执行”周期的连续循环中取指令、译码并执行。

Primary memory consists of RAM (volatile) and ROM (non-volatile). Cache memory is faster and located closer to the CPU.

主存储器包括 RAM（易失性）和 ROM（非易失性）。高速缓存速度更快，位于更靠近 CPU 的位置。

Secondary storage devices (HDD, SSD, optical disc) provide long-term, non-volatile storage.

二级存储设备（HDD、SSD、光盘）提供长期非易失性存储。

Binary representation uses base 2. Converting binary to hexadecimal: group bits into nibbles of 4.

二进制表示使用基数为 2。将二进制转换为十六进制：将位按 4 位一组分组。

Binary	Decimal	Hex
1101	13	D
1010 1111	175	AF

Logic gates perform Boolean operations: AND (∧), OR (∨), NOT (¬), NAND, NOR, XOR (⊕). Truth tables define their outputs.

逻辑门执行布尔运算：与门(∧)、或门(∨)、非门(¬)、与非门、或非门、异或门(⊕)。真值表定义了它们的输出。

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3. Networks | 网络

A LAN (Local Area Network) connects computers in a small geographical area; a WAN (Wide Area Network) spans large distances.

LAN（局域网）连接小地理区域内的计算机；WAN（广域网）跨越长距离。

The OSI model has 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, Application. TCP/IP model combines some layers.

OSI 模型有 7 层：物理层、数据链路层、网络层、传输层、会话层、表示层、应用层。TCP/IP 模型合并了部分层。

TCP provides reliable, connection-oriented communication with error checking; UDP is connectionless and faster, used for streaming.

TCP 提供可靠的、面向连接的通信，带有错误检查；UDP 是无连接的，速度更快，用于流媒体。

Encryption (SSL/TLS) secures data transmission; a firewall controls incoming/outgoing traffic.

加密（SSL/TLS）保护数据传输；防火墙控制进出流量。

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4. Computational Thinking & Problem-solving | 计算思维与问题解决

Computational thinking involves abstraction (hiding details), decomposition (breaking down problems), pattern recognition, and algorithm design.

计算思维包括抽象化（隐藏细节）、分解（拆解问题）、模式识别和算法设计。

Pseudocode uses keywords like INPUT, OUTPUT, IF…THEN…ELSE, LOOP…UNTIL, and assignment with ←.

伪代码使用诸如 INPUT、OUTPUT、IF…THEN…ELSE、LOOP…UNTIL 等关键字，并用 ← 进行赋值。

LINEAR_SEARCH(A, target)
  index ← 0
  found ← false
  WHILE index < LENGTH(A) AND NOT found
    IF A[index] = target THEN
      found ← true
    ELSE
      index ← index + 1
    END IF
  END WHILE
  IF found THEN
    OUTPUT index
  ELSE
    OUTPUT "Not found"
  END IF

线性搜索：从头到尾逐个比较，找到目标则返回索引，否则输出“未找到”。

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5. Programming Concepts | 编程概念

Variables store data; each has a data type (integer, real, string, Boolean).

变量存储数据；每个变量具有数据类型（整数、实数、字符串、布尔型）。

Control structures: sequence, selection (IF…ELSE, SWITCH), iteration (FOR, WHILE, REPEAT…UNTIL).

控制结构：顺序、选择（IF…ELSE, SWITCH）、迭代（FOR、WHILE、REPEAT…UNTIL）。

Methods (functions) encapsulate reusable code. Parameters may be passed by value or by reference.

方法（函数）封装可重用代码。参数可以按值传递或按引用传递。

Arrays store multiple elements of the same type; a 2D array acts like a table.

数组存储多个相同类型的元素；二维数组像一个表格。

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6. Object-Oriented Programming (HL) | 面向对象编程（HL）

OOP is based on classes and objects. A class is a blueprint; an object is an instance.

OOP 基于类和对象。类是蓝图；对象是实例。

Encapsulation hides the internal state and enforces access via methods (getters/setters).

封装隐藏内部状态，并通过方法（getter/setter）强制访问。

Inheritance allows a subclass to extend a superclass, promoting code reuse.

继承允许子类扩展超类，促进代码重用。

Polymorphism enables objects of different classes to be treated as objects of a common superclass, typically via method overriding.

多态使得不同类的对象可以被视为共同超类的对象，通常通过方法重写实现。

UML class diagrams use ‘+’ for public, ‘-‘ for private, ‘#’ for protected. A hollow triangle arrow indicates inheritance.

UML 类图中 ‘+’ 表示公有，’-‘ 表示私有，’#’ 表示受保护。空心三角箭头表示继承。

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7. Abstract Data Structures (HL) | 抽象数据结构（HL）

A stack is a LIFO (Last In, First Out) structure with operations push (add) and pop (remove).

栈是一种后进先出 (LIFO) 结构，包含 push（添加）和 pop（移除）操作。

A queue is FIFO (First In, First Out) with enqueue and dequeue.

队列是先进先出 (FIFO)，具有入队和出队操作。

A linked list consists of nodes, each containing data and a pointer to the next node.

链表由节点组成，每个节点包含数据和指向下一个节点的指针。

A binary tree has nodes with at most two children. A binary search tree maintains order: left subtree < root < right subtree.

二叉树每个节点最多有两个子节点。二叉搜索树维护顺序：左子树<根<右子树。

Graphs consist of vertices and edges; they can be directed or undirected. Recursion is often used in tree traversals (pre-order, in-order, post-order).

图由顶点和边组成；可以是有向或无向的。递归常用于树的遍历（先序、中序、后序）。

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8. Algorithms (HL) | 算法（HL）

Binary search operates on a sorted array by repeatedly halving the search interval. It has O(log n) time complexity.

二分搜索在有序数组上通过反复将搜索区间减半来操作，时间复杂度为 O(log n)。

Bubble sort compares adjacent elements and swaps them if out of order, repeating passes; O(n²) worst case.

冒泡排序比较相邻元素，若顺序错误则交换，重复遍历；最坏情况 O(n²)。

Merge sort divides the array, recursively sorts, then merges; O(n log n). It is stable.

归并排序先分割数组，递归排序后再合并；时间复杂度 O(n log n)，是稳定的。

Algorithm	Best	Average	Worst	Space
Linear Search	O(1)	O(n)	O(n)	O(1)
Binary Search	O(1)	O(log n)	O(log n)	O(1)
Bubble Sort	O(n)	O(n²)	O(n²)	O(1)
Merge Sort	O(n log n)	O(n log n)	O(n log n)	O(n)

常见算法复杂度表：最佳、平均、最坏时间复杂度及空间复杂度。

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9. Databases | 数据库

A relational database stores data in tables with rows and columns. Each table has a primary key that uniquely identifies records.

关系数据库以行为记录、列为字段的表存储数据。每个表都有一个主键，唯一标识记录。

SQL commands: SELECT … FROM … WHERE … to retrieve data; JOIN combines rows from multiple tables.

SQL 命令：SELECT … FROM … WHERE … 用于检索数据；JOIN 连接多个表的行。

Normalization reduces data redundancy by dividing tables and defining relationships (1NF, 2NF, 3NF).

规范化通过分割表和定义关系来减少数据冗余（1NF、2NF、3NF）。

A foreign key links a record in one table to a primary key in another, enforcing referential integrity.

外键将一个表中的记录链接到另一个表的主键，强制参照完整性。

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10. Modeling & Simulation (HL) | 建模与仿真（HL）

A model is a simplified representation of a real-world system. Computer simulations run models to predict behavior.

模型是真实世界系统的简化表示。计算机仿真运行模型以预测行为。

Discrete event simulation models systems where state changes occur at specific points in time.

离散事件仿真对状态在特定时间点发生变化的系统进行建模。

Validation ensures the model correctly represents the real system; verification checks that the model is correctly implemented.

验证确保模型正确表示真实系统；校核检查模型是否正确实现。

Monte Carlo simulation uses random sampling to compute results, useful for risk analysis and optimization.

蒙特卡洛仿真使用随机抽样来计算结果，适用于风险分析和优化。

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11. Web Science (HL) | 网页科学（HL）

The web relies on HTTP/HTTPS protocols for transferring hypertext documents. URLs identify resources.

网络依赖 HTTP/HT

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