Data structures & algorithms, from first principles

Every topic starts from a concrete analogy an 8th grader can follow, then builds up to full rigor: pseudocode, complexity analysis, edge cases, and real problems.

Phase 0 · Foundations

Big-O Notation Math Utilities Recursion Basics

Phase 1 · Arrays, Strings & Core Patterns

Arrays & Strings Fundamentals Two Pointers Sliding Window Prefix Sums Hashing Sorting Intuition

Phase 2 · Linked Lists

Singly Linked List Doubly Linked List

Phase 3 · Stacks, Queues & Monotonic Structures

Stack & Queue Monotonic Stack & Queue

Phase 4 · Trees

Binary Trees Binary Search Trees

Phase 5 · Heaps + Basic Greedy

Heaps & Priority Queue Basic Greedy

Phase 6 · Graphs

Graph Fundamentals Topological Sort Union-Find

Phase 7 · Backtracking

Phase 8 · Dynamic Programming

DP Fundamentals (1D)DP on Grids (2D)Knapsack Patterns LIS & String DP

Phase 9 · Remaining Topics

Tries Advanced Graph Algorithms Misc Algorithms