1. CS203 Lecture 14

2. Breadth First Traversal of a Binary Tree
Breadth First Search is not a wise way to find a particular element in a binary search tree, since it does not take advantage of the (log n) binary search we can get in a well-balanced tree.
However, the term is often used loosely to describe breadth-first traversal of an entire data structure. The most likely actual use case for BFS with a BST is to test whether your trees are being constructed correctly.
Lab 9 will include a method to do a BFS of your Binary Search Tree.
Here is the algorithm:
Create a permanent queue to hold all elements.
Create another, temporary queue to hold elements that you are processing to find the BFS order.
Add the root to the temporary queue.
As long as there are node references in the temporary queue, poll them one at a time, add them to the permanent queue, and add any left or right references to the temporary queue
When the last node is polled from the temporary queue, the permanent list is complete. 2

3. Create a queue for unvisited nodes and a list for visited nodes
Breadth First Traversal
Create a queue for unvisited nodes and a list for visited nodes
Put the starting node at the back of the queue.
While the queue is not empty:
Take the front item of the queue and add it to the visited list.
Create a list of that nodes neighbors nodes. Add those which have not already been visited to the back of the queue.
The next two slides show BF traversal of a graph. Think about how to do this with a BST.
This slide and the next two use material from

4. Breadth First Traversal

5. Breadth First Traversal

6. Quick-Sort
Quick-Sort 
4 2  2 4
7 9  7 9
2  2
9  9
Quick-Sort