Breadth First Search

When there's relationship b/w nodes on the same level logically.

Basic method:

1. Data structure: Maintain a FIFO queue, put in all traversed nodes that have not been expanded, and then the other nodes on the same level.

2. Initial state: start node.

3. Expand the node, visit/print its value.

4. Generate its neighbor nodes, reach out.

5. Termination condition: queue.isEmpty()

6. Optionally deduplicate visited nodes for graphs. Each node could be generated multiple times, but should only be expanded once.

7. Explicit graph vs. Implicit graph