Reference library 10 cheatsheets · updated September 2026

Cheatsheets

Reference cards built from real interview questions and production code. Each one fits on one screen, with complexity notes and common gotchas.

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Java

4 sheetsSee track →
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Java Collections Cheat Sheet

Quick reference for Java Collections — ArrayList, LinkedList, HashMap, Tree…

6 sectionsOpen →

Java Streams API Cheat Sheet

Complete Java Streams cheat sheet — intermediate and terminal operations, c…

5 sectionsOpen →

JVM Memory Model Diagram

Visual diagram of JVM memory areas — Heap, Young/Old generation, Metaspace,…

7 sectionsOpen →

How HashMap Works Internally

Illustrated diagram of Java HashMap internals — hashing, bucket array, coll…

7 sectionsOpen →

Python

2 sheetsSee track →
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Python Built-in Functions Cheat Sheet

Complete reference for Python built-in functions — type conversion, math, s…

6 sectionsOpen →

Pandas Cheat Sheet

Quick reference for Pandas — DataFrame creation, selection, filtering, grou…

10 sectionsOpen →

Database

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SQL Joins Cheat Sheet

Visual reference for all SQL JOIN types — INNER, LEFT, RIGHT, FULL OUTER, C…

6 sectionsOpen →

DevOps

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Docker Commands Cheat Sheet

Essential Docker commands reference — containers, images, volumes, networks…

7 sectionsOpen →

System Design

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Microservices Cheat Sheet

Visual reference for microservices architecture — API gateway, services, me…

7 sectionsOpen →

DSA

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Data Structures & Algorithms Cheat Sheet

Complete DSA quick reference — time/space complexities, Java implementation…

18 sectionsOpen →
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