### Comp 271-400 Week 4

Cuneo 311, 4:15-8:15

Welcome

**Readings**:

Bailey chapter 5 section 2 on recursion

Bailey chapter 6, on sorting.

Bailey chapter 9 section 4 on Singly Linked Lists

Bailey chapter 15, section 4, on Hash Tables.

Bailey chapter 3, on a Vector class

Morin 3.1: Singly Linked Lists

Morin 5.1: Chained Hash Table

Morin Chapter 11: sorting (Merge-sort and Quicksort only)

Primary text: Bailey, online, and maybe Morin, also online.

## Exam next week

We will start the exam around 6:20. You'll have (almost) two hours, but
you shouldn't need all that time.

The study guide is on Sakai. Answers will be posted at the end of this
week.

You can bring up to **three pages** (sides) of your own **printed**
or handwritten notes. You will also receive a copy of StrList.java, which
includes examples of basic Java constructions.

There's an algorithmic reason why quicksort's speed is affected by whether
the data is already sorted: if we pick data[left] as the pivot in a sorted
array, we'll partition into an empty left half and a right half of size N-1.

But why should *mergesort* be faster if the data is already sorted?
The algorithm executes exactly the same steps!

Demo: pldsorting/DualMerge.java, prev/sortspeed
Related question: why is insertion sort faster than selection sort?

#### Radix Sort

133 312
121 213 122
211 321 132 223
332

Naive approach: bucketize on the first digit, then sort the buckets
recursively.

1337 approach: bucketize on the last digit, concatenate, bucketize on
second-to-last digit, concatenate, bucketize on the first digit
(third-to-last digit)

**in-class lab 1**

Install expressionsij.zip.

Trees

binary trees

insertion and search

traversal

tree-based dictionaries

Lab 4

### Recursion

Recursion starts at Bailey page 94

See recursion.html
and recursion1ij.zip.

- Expressions
- Assignment
- Framework: parsing statements plus
*syntax-directed actions*.
- Exponentiation?