Learn about data structures.

Start with exercises 1–3: they introduce the new techniques for this level. After that, pick from the additional exercises: 4–5 are ⭐ (easier), 6–7 are ⭐⭐ (medium), and 8–9 are ⭐⭐⭐ (harder). Aim for at least ⭐⭐⭐⭐ in total before moving on to the next level.

You can use this programming guide as a reference while you work through the exercises.