Julie explains procedural recursion and introduces permute code. She goes through another example of recursive code line by line, explaining each component. Recursive backtracking and it's usefulness are discussed. The example of placing several queen chess pieces on a board where none of them can attack the other is then demonstrated.
This course (CS 106B) is the successor to CS 106A and covers more advanced programming topics such as recursion, algorithmic analysis, and data abstraction. It is taught using the C++ programming language, which is similar to both C and Java. In the past when both CS 106A and CS106B were taught in C/C++, the coupling between the two classes was very tight and it was unheard for students to take CS106B without having completed our CS 106A (we recommended CS 106X instead). Nowadays, some students do go straight into CS106B, this is typically appropriate for a student who done well in an intro programming course (e.g., scored 4 or 5 on the CS AP exam or earned a good grade in a college course) and has sufficient familiarity with good programming style and software engineering issues (at the level of CS 106A) to use this understanding as a foundation on which to tackle advanced topics.