Computer Science Cheat Sheet

The core ideas of Computer Science distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Algorithms

An algorithm is a finite, well-defined sequence of instructions for solving a problem or performing a computation. Algorithms are the heart of computer science and can be analyzed for their correctness, efficiency, and resource usage. Common categories include sorting algorithms, search algorithms, graph algorithms, and dynamic programming approaches.

Data Structures

A data structure is a specialized format for organizing, storing, and accessing data efficiently. Choosing the right data structure is critical because it directly affects the performance of algorithms that operate on the data. Common data structures include arrays, linked lists, stacks, queues, hash tables, trees, and graphs.

Big O Notation

Big O notation is a mathematical notation used to describe the upper bound of an algorithm's time or space complexity as the input size grows. It abstracts away constant factors and lower-order terms to focus on the dominant growth rate, allowing developers to compare algorithms and predict scalability.

Object-Oriented Programming

Object-oriented programming (OOP) is a programming paradigm based on the concept of objects, which bundle data (attributes) and behavior (methods) together. OOP relies on four key principles: encapsulation, abstraction, inheritance, and polymorphism. These principles promote modular, reusable, and maintainable code.

Recursion

Recursion is a technique where a function calls itself to solve smaller instances of the same problem until it reaches a base case. It is a natural fit for problems that have a self-similar structure, such as tree traversal, factorial computation, and divide-and-conquer algorithms. Every recursive solution must have at least one base case to prevent infinite recursion.

Databases

A database is an organized collection of structured data managed by a database management system (DBMS). Relational databases use tables with rows and columns and are queried using SQL, while NoSQL databases use flexible schemas such as documents, key-value pairs, or graphs. Databases ensure data integrity, support concurrent access, and enable efficient querying of large datasets.

Operating Systems

An operating system (OS) is software that manages computer hardware and provides services for application programs. It handles process scheduling, memory management, file systems, device drivers, and security. The OS acts as an intermediary between users and hardware, enabling multiple programs to run concurrently and share resources safely.

Computer Networking

Computer networking is the practice of connecting computers and devices to share resources and communicate. Networks operate using layered protocol models such as TCP/IP, where each layer handles a specific responsibility from physical transmission to application-level communication. Key concepts include IP addressing, routing, DNS, HTTP, and encryption.

Machine Learning Basics

Machine learning is a subfield of artificial intelligence where systems learn patterns from data rather than being explicitly programmed. Supervised learning uses labeled training data to make predictions, unsupervised learning finds hidden structure in unlabeled data, and reinforcement learning trains agents through trial-and-error with rewards. Models are evaluated on their ability to generalize to unseen data.

Software Engineering

Software engineering is the systematic application of engineering principles to the design, development, testing, deployment, and maintenance of software. It encompasses methodologies like Agile and Waterfall, practices such as version control, code review, and continuous integration, and architectural patterns that help teams build reliable, scalable systems. The goal is to produce high-quality software efficiently and predictably.

Key Terms at a Glance

Abstraction:The process of hiding complex implementation details and exposing only essential features, allowing users to interact with systems at a higher level without understanding internal workings.

Algorithm:A finite, well-defined sequence of instructions designed to perform a specific task or solve a particular problem, which can be analyzed for correctness and efficiency.

API (Application Programming Interface):A set of defined rules and protocols that allow different software applications or components to communicate and exchange data with each other.

Binary:A base-2 number system using only the digits 0 and 1, serving as the fundamental representation of data in digital computing systems.

Boolean:A data type with only two possible values, true or false, named after mathematician George Boole. Used extensively in conditional logic and control flow.

Cache:A high-speed storage layer that stores a subset of frequently accessed data so future requests can be served faster than accessing the primary data source.

Compiler:A program that translates source code written in a high-level programming language into lower-level machine code or intermediate code that a computer can execute.

Concurrency:The ability of a system to handle multiple tasks or processes in overlapping time periods, which may involve parallelism on multi-core systems or interleaved execution on a single core.

Data Structure:A specialized format for organizing, managing, and storing data that enables efficient access and modification according to specific use cases.

Debugging:The process of identifying, isolating, and fixing errors (bugs) in software code to ensure the program behaves as intended.

Encryption:The process of converting plaintext data into ciphertext using an algorithm and key, making it unreadable to unauthorized parties and protecting data confidentiality.

Graph:A non-linear data structure consisting of vertices (nodes) connected by edges, used to model relationships and networks such as social connections, road maps, and web links.

Heuristic:A problem-solving approach that uses practical methods or shortcuts to produce solutions that may not be optimal but are sufficient for reaching an immediate goal.

Inheritance:An OOP mechanism where a new class (subclass) derives attributes and methods from an existing class (superclass), promoting code reuse and hierarchical organization.

Interpreter:A program that executes source code line by line at runtime, translating each statement into machine actions on the fly rather than compiling the entire program beforehand.

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