1. Lecture 18
CSE 331
Oct 12, 2011

2. Mid-term related stuff
Solutions will not be handed out
Jesse will discuss them in his recitations
We will write solution sketches on your graded mid terms

3. Questions?

4. Main Steps in Algorithm Design
Problem Statement
Problem Definition n!
Algorithm
“Implementation”
Data Structures
Analysis
Correctness+Runtime Analysis

5. A tool to define problems
Where do graphs fit in?
Problem Statement
A tool to define problems
Problem Definition
Algorithm
“Implementation”
Data Structures
Analysis
Correctness+Runtime Analysis

6. Three general techniques
Rest of the course
Problem Statement
Problem Definition
Three general techniques
Algorithm
“Implementation”
Data Structures
Analysis
Correctness+Runtime Analysis

7. Greedy algorithms Build the final solution piece by piece
Being short sighted on each piece
Never undo a decision
Know when you see it

8. End of Semester blues
Can only do one thing at any day: what is the maximum number of tasks that you can do?
Write up a term paper
Party!
331 homework
Exam study
331 HW
Project
Monday
Tuesday
Wednesday
Thursday
Friday

9. Greedily solve your blues!
Arrange tasks in some order and iteratively pick non-overlapping tasks
Write up a term paper
Party!
Exam study
331 HW
Project
Monday
Tuesday
Wednesday
Thursday
Friday

10. Ordering is crucial Order by starting time Write up a term paper
Algo =1
Party!
Exam study
331 HW
Project
Monday
Tuesday
Wednesday
Thursday
Friday

11. Ordering by least conflicts doesn’t work
Another attempt
Order by duration
Ordering by least conflicts doesn’t work
Algo =1
Monday
Tuesday
Wednesday
Thursday
Friday

12. Order tasks by their END time
The final algorithm
Order tasks by their END time
Write up a term paper
Party!
Exam study
331 HW
Project
Monday
Tuesday
Wednesday
Thursday
Friday

13. Questions?

14. Today’s agenda
Prove the correctness of the algorithm

15. Formal Algorithm R: set of requests Set A to be the empty set
While R is not empty
Choose i in R with the earliest finish time
Add i to A
Remove all requests that conflict with i from R
Return A