1. CS 280 Data Structures Professor John Peterson

2. Project “Tree 1” Questions? Let’s look at my test cases

3. Search Trees So far, we’ve looked at searching a tree, adding a node to a tree in sorted order, and traversing the tree. What about deleting a node? That’s a lot harder!

4. Method Design Although we do the delete destructively, we still need to use a functional style of method call – that is, always return something instead of just doing something. Why?? Tree delete(int x, Tree t) { What are the base cases? Let’s get started on the board.

5. Deleting a node with two kids This is the hard part – how to delete something like the 5 in 5 3 8 2 4 7 9 We have two possible choices: promote either the 4 or 7 up to where the 5 is. We’ll arbitrarily choose the right (7). So the plan is to create an aux method to delete the lowest element in a tree and return it. I’ll use a Pair to allow the method to give me a value and a tree at the same time.

6. Deleting the Lowest Two cases: Left is null – what then? Left is not null – what then?