How to use this book

F O U N D A T I O N S

Solving LeetCode problems is not about being a genius. It is a skill, and like any skill it breaks down into a small number of patterns that show up again and again. Once you can recognize the pattern, most problems become variations of something you have already done.

This book is organized around those patterns, not around random problems. Each chapter follows the same shape so you always know what you are getting: The idea in plain English. What the pattern actually is, without jargon.

When to reach for it. The signals in a problem statement that tell you "this is the one." A picture. Almost every pattern is easier to see than to read.

A template. The skeleton of code you can adapt, so you are not starting from a blank page.

Worked examples in both Python and Java, with the thinking spelled out.

Tricks and traps that save you time or stop you from failing on edge cases.

H O W T O A C T U A L L Y L E A R N T H I S

Reading is not practice. The loop that works is simple: read the pattern here, then go solve three or four problems that use it before moving on. Struggle for about twenty minutes before looking at a hint. When you get stuck and read the answer, close it and rewrite the solution from memory. If you cannot rewrite it, you have not learned it yet.

You do not need to read this front to back. If you already know arrays and want trees, jump there.

But the Foundations chapters, especially how to approach a problem and how to think about time complexity, pay off in every single chapter after them, so start there if you are newer to this.