Phones off Signs out Picnic on Friday 

1. Phones off Signs out Picnic on Friday 

3. Preliminaries • Attendance sheets • I remembered! • HW1 due tonight • progress report • Stage 1 due on Friday • progress report

4. Today • Finish off discussion Bag’s iterator class • For-each loop: syntactic sugar • Software design issues • In context of list definition • Recursion • In context of list definition

5. Lists • We’ve seen an array-based implementation of a Collection, the Bag. • ArrayList is very much the same. • We’ll take a short tour of the code

6. Advantage of an array-based implementation: • fast access to a specific index • typically less space usage than other options • Disadvantage of an array-based implementation: • can be expensive to insert items • resizing is an expensive operation

7. Amortization • Resizing of array-based data structures involves a tradeoff: • many insertions (as in our Bag) are very efficient since no allocation of space is required (an array is allocated as a big block of memory) • some insertions (as in our Bag) are very expensive since resizing must take place

8. Linked List • A linked list is a list implementation which spreads out the cost of space allocation evenly to all insertions. • Each insertion involves allocation of space

9. Advantages/Disadvantages • Advantages • predictable cost of insertion • efficient insertion at any point in structure • Disadvantages • extra space required to store links • inefficient indexing

10. Comparison of storage • A pair has a first and a second element • When pairs are used to construct lists, • the first is called the “head” or the “car” • the second is called the “tail”, “rest” or “cdr” • the pair is called a “cons cell” or simply a “cons”.