CSC 212 – Data Structures Lecture 37: Course Review

Final Exam Friday, Dec. 15 from 3:15 – 5:15 in OM 205 Plan for exam to take full 2 hours  Talk to me if this is a major problem Exam covers material from entire semester  Format like 2 midterms  Still open-book, open-note, closed-computer

Design computational solutions  Decompose a problem into logically grouped subprograms  Develop and analyze algorithms Program well  Code in a high-level language  Debug a program  Write and use a test plan  Document a program  Work independently Organize data for effective use  Use fundamental data structures  Implement data structures Understand the role of computing and the computer professional  Present or explain ideas  Weigh different solutions and explain or argue why one was preferable Objectives Met in CSC212 Design computational solutions  Decompose a problem into logically grouped subprograms  Develop and analyze algorithms Program well  Code in a high-level language  Debug a program  Write and use a test plan  Document a program  Work independently Organize data for effective use  Use fundamental data structures  Implement data structures Understand the role of computing and the computer professional  Present or explain ideas  Weigh different solutions and explain or argue why one was preferable

What Gets Inherited and How All fields & methods (members) inherited  Public members accessed as if declared in subclass (but they should not be!)  Private members cannot be accessed  Protected members used as if subclass declared them as private (but, do not do this!) Subclasses can override/overload method  Call method defined for instance’s type Subclasses can hide field  Use the field defined for variable’s type

Exceptions in Java Throw exception when problem detected  Must instantiate instance before throwing Handle by catching exception  Only catch exceptions you want to handle Method lists exceptions thrown via throws  Include any exception not caught  Does not matter if method was originator

Abstract methods cannot have a body  IOU that subclasses will define the method Class with abstract methods is abstract  Cannot be instantiated, but can be extended  Can have fields & methods Interface declares abstract methods  All methods are public abstract methods Abstract Methods

Arrays vs. Linked Lists Two alternate ways to hold data  Not ADTs, but specific implementations Arrays generally offer quick access times, but hard to maintain and resize Linked lists offer flexible sizing, but access times can be slow  Can be singly, doubly, or circularly linked

Queues, Stacks, & Deques Offer simple means of tracking elements  Like a line, Queues are first-in, first-out  Stacks are last-in, first-out  Deques can be accessed from either end Cannot access interior elements  No way of searching for an element either Implemented with either array or linked list  Arrays can violate unlimited space guarantee

Iterators & Iterables Important interfaces defined by Java: import java.util.Iterator; import java.lang.Iterable; public interface Iterator { E next(); boolean hasNext() throws NoSuchElementException; void remove() throws UnsupportedOperationException; } public interface Iterable { Iterator iterator(); }

More Iterator & Iterable Use Iterator to abstract processing Iterator it;... for (it = myList.iterator(); it.hasNext(); ) { Integer i = it.next();... } Process Iterable objects in an even easier way... for (Integer i : myList) {... }

Lists List is Iterable collection of elements  Can now access any element in collection  Different lists provide other accessor methods IndexList access using 0-based ranks  Not the same as array -- ranks can change PositionList access via relative position  Relies on Position ADT to hold elements Sequence combines two lists & Deque

How Computer Normally Works I’ll have a Manhattan No problem. That’ll be $2 billion

Working With Map & Dictionary I’ll have a Manhattan No problem. That’ll be $2 billion key value

Maps & Dictionaries Rely on Entry ADT -- key & value pair Maps have at most 1 Entry with any key  New Entry replaces previous Entry with key  Remove Entry by specifying its key Entrys in Dictionary can share key  New Entry does not affect others with that key  Remove Entry by specifying key AND value

Map & Dictionary Implementation Many possible implementations possible  Sequence with elements kept in sorted order  Sequence with elements kept in unsorted order  Hash Table (which is not an ADT) Hash table stores all of the Entrys  Hash function uses key to compute integer from 0 to size of table - 1  Goal is storing entry (k, v) at index h(k)

Collisions When implemented with hash table & two Keys share hash code Three commonly used handling schemes  Separate chaining: table contains Lists of entries hashed to that index  Linear probing: loop through array looking for first open array location  Double hashing: plug key into another hash function to find empty array location

Sets & Partitions Sets implement at least three operations  intersect, union, & subtract  Constructor others depend on how Set used Set’s operations rely on instances of subclasses of Merge Partition is first use of Set  Instances hold collection of disjoint Sets  Set’s constructor must take single element

Quick-Select & Pattern Matching Quick-Select finds n th element in Sequence  Uses divide-and-conquer for speed  Honestly, not a lot to ask about it Know the pattern matching algorithms  When & why we may want to use one over the others  Also know how to perform their actions -- mostly “trained monkey” work

Hints for Studying The exam will NOT require:  Memorizing ADT’s methods  Memorizing Node implementations  Memorizing big-Oh time proofs  (Recursion) The exam WILL require:  Knowing what the methods do  Be able to implement the methods  Computing big-Oh time complexity

Studying For the Exam 1. What does the ADT do? What are real-world analogues for it? 2. How is the ADT used? What applications use this ADT? How do they use it and why? 3. Can you explain examples’ answers? Keep reviewing material until you can do this cold 4. How do we implement the ADT? Why is it implemented in that way? What are the performance tradeoffs?

Before Next Lecture… CSC212 Final Exam: Fri., Dec. 15 from 3:15–5:15 in OM 205 Bring 1 (or more) pencils to the exam Do well on all your finals Have a good Christmas break Get ready for new term of challenges & fun