1. Professor John Peterson
CS 280 Data Structures
Professor John Peterson

2. Next Project
Merge Sort. Read about this and be ready to talk about it Friday.

3. Example 5
null 7
Next
Data a b

4. Example 5 null 7 Link Data a b
Link<Integer> a = new Link<Integer>()
a.data = 5
Link<Integer> b = new Link<Integer>()
b.data = 7
a.next = b

5. Example 5 7 null 3 Link Data a b Evaluate a.next a.data a.next.data
b.next.next
a.next.next.data

6. Example 5 7 null 3 Next Data a b What does this do? b.next.next = a;
b = b.next; a.data = a.data + 1; b.data = b.data + b.next.data; a = b.next;

7. Aliasing Exercises
Link<Integer> a = new Link<Integer> (); Link<Integer> b = new Link<Integer> (); Link<Integer> c = new Link<Integer> (); Link<Integer> d = a; a.data = 2; b.data = 3; c.data = 4; d.data = 5; a.next = b; b.next = c; c.next = a; a.next.data = 6; b.next.next.data = 7; print(d.data);

8. Avoiding Aliasing
One style of programming avoids issues involving aliasing: non-destructive (functional) programming.
Once you create structure, you never change it.
This allows you to ignore the difference between objects and values

9. Embracing Aliasing
If aliasing is present, you need to know that changes are seen by all objects sharing a reference (pointer) to an object.
This might be just what you want!
You need to be VERY aware of where pointers point.

10. Basic Recursive Techniques
Decide what information you need at each step – if you need to initialize a new value, this requires an auxiliary function.
Develop a test to determine whether the recursion is done
Update parameters at the recursive calls.

11. Auxiliary Functions
These are an IMPORTANT part of recursion! No nice way to do these in Java – place these in the class next to the recursive functions and make them private (why?)

12. Example
Lets write a method to create a list of N copies of some value. Which is easier to read / write? Harder: Create a list containing integers from 1 to N. Note the use of an auxiliary function in the recursive version! Note the special case in the iterative version.

13. Duplicate
public Link<Integer> duplicate(int n, int v) { if (n <= 0) return null; return new Link<Integer>(v, duplicate(n-1, v)) }

14. upto
public Link<Integer> upto(int n) { return upto1(1, n); } public Link<Integer> upto1(int i, int n) { if (i > n) return null; return new Link<Integer>(i, upto1(i+1, n)) }