Data Structures & Algorithms
Data structures and algorithms for coding interviews: a plain-language lesson per pattern, then interview-style problems from easy to hard, solved in Python or JavaScript.
14 sections · 210 problems · part of Interview Prep
Free lesson: Arrays
A row of values you reach by position. Arrays are the base most other structures are built on, and the most common interview topic.
13 more sections and 208 more problems, easy to hard, are in Interview Prep.
Practice in the browser
After signing in, every problem runs in your browser, in Python or JavaScript, with hints and worked solutions. The free ones need only an account.