Coding interviews focus on testing your ability to write good code.
Some companies focus a lot of algorithms and data structures in this interview. For example: Google, Facebook, Uber, Lyft, Palantir, Twitter, and DeepMind.
Our general recommendations:
We recommend learning about or brushing up your knowledge on data structures and algorithms in the following order: Common data structures and algorithms.
Consider getting the latest edition of the Cracking the Coding Interview by Gayle Laakmann Mcdowell. The book may look big in its printed version, but it is written in a friendly way and most of the book is just code with solutions to problems. Here is a secret - you can skip them and just read the theory part. For problem-solving see recommendations in other sections.
Consider buying a small whiteboard. This can help you with mock interviews before onsite interviews and will set you apart from others in case you will have a video interview rather than a phone interview.