Overview

The Algorithms Guide

Five projects you completed, explained from scratch: why the solution is the solution, not just how to type it. Every piece of code here was actually run, and every output below is real.

📘6 parts🧪all code executed🌓light and dark🌍Arabic and English

Why this guide?

The exercise gives you the requirement and the expected answer. This guide gives you the thinking in between: where to start, which structure fits, and why this one and not that one.

How to read it

Each part opens with the prerequisites, then the concepts, then the diagrams, then the solution step by step. Do not jump to the code, the code is the shortest and least important thing on the page.

Cards and questions

Each part ends with flashcards you flip by clicking, a multiple-choice question, and five "check your understanding" questions with hidden answers. Use them before you say "I get it".

A warning

The code here is for understanding, not for copying. Copy a solution without understanding it today, and you will face the same problem in an interview next month.

The track map

The five projects are not independent: each one builds a skill the next one uses. A dashed line means "this skill carries over there".

StartKey idea

The project order and the skill each one adds.

Topics

1🔺 Pascal's TriangleHow to build a list of lists row by row, why every number is the sum of the two above it, and where off-by-one bugs come from.O(n²)2🔐 LockboxesA puzzle that looks like keys but is really your first graph search: starting from box zero, what can you reach?O(n+k)3✂️ Minimum OperationsThe “copy all and paste” puzzle that turns, after two lines of thinking, into prime factorisation.O(√n)4📊 Log ParsingYour first time reading an endless stream instead of a file: line by line, skipping the malformed, printing every ten lines.O(1) memory 5🔤 UTF-8 ValidationYour first serious meeting with bits: how UTF-8 encodes a character in one to four bytes, validated with a state machine.O(n)6♛ N QueensYour first real backtracking: build the solution row by row and retreat the moment it is impossible, instead of trying millions of arrangements.backtracking

What you actually walk away with

Projects are forgotten; skills stay. These five are what a senior engineer asks you about in a code review:

StartOutcome

The transferable skills from these five parts.

The one rule that ties all five togetherBefore writing a line, ask: "what shape is this problem?" Pascal's triangle is a table, lockboxes is a graph, minimum operations is factorisation, log parsing is a stream, and UTF-8 is a state machine. Naming the right shape turns a hard problem into a known one.

Parts added to this track

Part	Topic	You learn
7	Rotating a 2D matrix	Grid indices, the transpose, and working in place
8	Making change and dynamic programming	Greedy and when it fails, the DP table, and the base case
9	Sequential API requests in order	Promises, await in a loop, Promise.all and ordering
10	Islands in a grid: neighbours and edges	The four neighbours, bounds, DFS and counting by edges
11	Prime numbers and a removal game	The sieve, prefix sums, and analysing turn-based games

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Overview

The Algorithms Guide

The track map

Topics

What you actually walk away with

Parts added to this track

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