CSC 212 – Data Structures

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

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 • 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 • 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

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> { E next(); boolean hasNext() throws NoSuchElementException; void remove() throws UnsupportedOperationException;}public interface Iterable<E> { Iterator<E> iterator();}

More Iterator & Iterable • Use Iterator to abstract processing Iterator<Integer> 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 That’ll be $2 billion No problem.

Working With Map & Dictionary I’ll have a Manhattan That’ll be $2 billion No problem. 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 nth 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 • What does the ADT do? • What are real-world analogues for it? • How is the ADT used? • What applications use this ADT? • How do they use it and why? • Can you explain examples’ answers? • Keep reviewing material until you can do this cold • 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

CSC 212 – Data Structures