LEVEL 2 OF 5

Core Data Structures

Think in links, stacks, and recursive calls.

Linked List

Follow identity-based links between nodes; position is reached by traversal rather than indexing.

The most recent unfinished task must be resolved first.

Process items in the order they were discovered. The oldest unfinished item leaves first.

Remove or add candidates at either end to maintain a useful frontier, such as decreasing values for window maxima.

Solve a smaller instance and keep unfinished work in a call frame.

Explore a decision tree by choosing an option, solving the smaller remaining task, and undoing the choice before trying another option.

Follow a deterministic sequence at two speeds to detect a cycle without storing every visited state.