DSA — From Zero to Strong

What you will learn

Starting from absolutely nothing — no assumed knowledge. Every concept explained simply. Math taught when needed. One topic per day. No rush.

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The Full Roadmap

Phase 0 — Foundations (Before DSA)

Understanding what DSA even is, and the small amount of math you need.

Day	File	Topic
1	phase-0-foundations/day-01-what-is-dsa.md	What is DSA? Why learn it?
2	phase-0-foundations/day-02-math-exponents.md	Math: Exponents (powers)
3	phase-0-foundations/day-03-math-logarithms.md	Math: Logarithms
4	phase-0-foundations/day-04-math-modulo.md	Math: Modulo (remainder)

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Phase 1 — Big O Notation

How to measure if your code is fast or slow. You need this before anything else.

Day	File	Topic
5	phase-1-big-o/day-05-big-o-intro.md	What is Big O?
6	phase-1-big-o/day-06-big-o-common.md	O(1), O(n), O(n²), O(log n), O(n log n)
7	phase-1-big-o/day-07-big-o-practice.md	Reading code and finding its Big O

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Phase 2 — Arrays

The most basic and most used data structure.

Day	File	Topic
8	phase-2-arrays/day-08-arrays-intro.md	What is an array? How does it work in memory?
9	phase-2-arrays/day-09-arrays-methods.md	Array methods and their Big O
10	phase-2-arrays/day-10-arrays-problems-1.md	First easy problems
11	phase-2-arrays/day-11-arrays-two-pointers.md	Two Pointers technique
12	phase-2-arrays/day-12-arrays-sliding-window.md	Sliding Window technique
13	phase-2-arrays/day-13-arrays-prefix-sum.md	Prefix Sum technique

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Phase 3 — Hash Maps

The second most important data structure. Makes many problems easy.

Day	File	Topic
14	phase-3-hashmaps/day-14-hashmaps-intro.md	What is a Hash Map? How does it work?
15	phase-3-hashmaps/day-15-hashmaps-problems-1.md	Frequency counter pattern
16	phase-3-hashmaps/day-16-hashmaps-problems-2.md	More hash map problems

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Phase 4 — Strings

Working with text.

Day	File	Topic
17	phase-4-strings/day-17-strings-intro.md	Strings — how they work, methods
18	phase-4-strings/day-18-strings-problems-1.md	Palindromes, anagrams, reversal
19	phase-4-strings/day-19-strings-problems-2.md	Substring problems

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Phase 5 — Linked Lists

A different way to store a sequence of items.

Day	File	Topic
20	phase-5-linked-lists/day-20-linked-lists-intro.md	What is a Linked List?
21	phase-5-linked-lists/day-21-linked-lists-problems-1.md	Traversal, reverse, find middle
22	phase-5-linked-lists/day-22-linked-lists-problems-2.md	Cycle detection, merge

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Phase 6 — Stacks & Queues

Two structures with strict rules about how you add/remove items.

Day	File	Topic
23	phase-6-stacks-queues/day-23-stacks-intro.md	What is a Stack?
24	phase-6-stacks-queues/day-24-queues-intro.md	What is a Queue?
25	phase-6-stacks-queues/day-25-stacks-queues-problems.md	Problems using stacks and queues

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Phase 7 — Recursion

Functions that call themselves. Needed for trees, graphs, and more.

Day	File	Topic
26	phase-7-recursion/day-26-recursion-intro.md	What is recursion? How does it work?
27	phase-7-recursion/day-27-recursion-problems-1.md	Basic recursion problems
28	phase-7-recursion/day-28-recursion-problems-2.md	Harder recursion problems

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Phase 8 — Sorting Algorithms

How to put things in order — and why some ways are faster than others.

Day	File	Topic
29	phase-8-sorting/day-29-bubble-sort.md	Bubble Sort (simple, slow)
30	phase-8-sorting/day-30-selection-insertion-sort.md	Selection Sort & Insertion Sort
31	phase-8-sorting/day-31-merge-sort.md	Merge Sort (fast, uses recursion)
32	phase-8-sorting/day-32-quick-sort.md	Quick Sort (fast, commonly used)

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Phase 9 — Searching

How to find things efficiently.

Day	File	Topic
33	phase-9-searching/day-33-linear-search.md	Linear Search
34	phase-9-searching/day-34-binary-search.md	Binary Search (O(log n) — very fast)
35	phase-9-searching/day-35-binary-search-problems.md	Binary search problems

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Phase 10 — Trees

Hierarchical data. Used everywhere (file systems, databases, HTML DOM).

Day	File	Topic
36	phase-10-trees/day-36-trees-intro.md	What is a Tree? Terminology
37	phase-10-trees/day-37-binary-search-tree.md	Binary Search Tree
38	phase-10-trees/day-38-tree-dfs.md	DFS — Depth First Search on trees
39	phase-10-trees/day-39-tree-bfs.md	BFS — Breadth First Search on trees
40	phase-10-trees/day-40-tree-problems.md	Tree problems

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Phase 11 — Graphs

The most general structure. Everything connects to everything.

Day	File	Topic
41	phase-11-graphs/day-41-graphs-intro.md	What is a Graph?
42	phase-11-graphs/day-42-graphs-bfs-dfs.md	BFS and DFS on graphs
43	phase-11-graphs/day-43-graphs-problems.md	Graph problems

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Phase 12 — Dynamic Programming

Breaking big problems into smaller ones. Most feared topic — made simple.

Day	File	Topic
44	phase-12-dynamic-programming/day-44-dp-intro.md	What is DP? Memoization
45	phase-12-dynamic-programming/day-45-dp-tabulation.md	Bottom-up DP (tabulation)
46	phase-12-dynamic-programming/day-46-dp-classic-problems.md	Classic DP problems
47	phase-12-dynamic-programming/day-47-dp-more-problems.md	More DP problems

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Phase 13 — Advanced Patterns

Techniques that appear in many interview problems.

Day	File	Topic
48	phase-13-patterns/day-48-two-pointers-advanced.md	Two Pointers — advanced
49	phase-13-patterns/day-49-sliding-window-advanced.md	Sliding Window — advanced
50	phase-13-patterns/day-50-backtracking.md	Backtracking

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Rules for Learning DSA

1. Do not skip days. Each day builds on the previous one.
2. Read slowly. Don't rush to the code. Understand the idea first.
3. Write the code yourself. Don't copy-paste. Type it out.
4. Solve the practice problems before looking at the answer.
5. If something is unclear — re-read it. Then re-read it again.

How each file is structured

Every day file has:

• Simple explanation — what is this thing, in plain English
• Real-world analogy — connect it to something you already know
• How it works — step by step, no skipping
• JavaScript code — with every line explained
• Practice problems — you solve these yourself
• Solutions — with full explanation