1. Lecture 21
CSE 331
Oct 19, 2011

2. Technical Interviews (Sean)
- Thursday October 27th
- 6:30 – 9:00 PM
- Faculty comments
- Free Stuff!!!
- Sign-Ups

3. Online office hrs tonight 10:00pm

4. Scheduling to minimize lateness
n jobs: ith job (ti,di)
At most one job at any time
start time: s
Schedule the n jobs: ith job gets interval [s(i),f(i)=s(i)+ti)
Not the sum
Algo picks s(i)
GOAL: Minimize MAXIMUM lateness
Lateness of job i, li = max(0,f(i)-di)

5. The Greedy Algorithm f=s For every i in 1..n do
(Assume jobs sorted by deadline: d1≤ d2≤ ….. ≤ dn)
f=s
For every i in 1..n do
Schedule job i from s(i)=f to f(i)=f+ti
f=f+ti

6. Solving end of Semester blues
Term paper
Exam study
Party!
331 HW
Max lateness = 2
Project 2
Party!
Exam study
331 HW
Term paper
Project
Monday
Tuesday
Wednesday
Thursday
Friday

7. Today’s agenda Prove that the greedy schedule output
minimizes the maximum lateness

8. Two definitions for schedules
Idle time
Max “gap” between two consecutively scheduled tasks
Idle time =1
Idle time =0 i j
Inversion
(i,j) is an inversion if i is scheduled before j but di > dj i j
f=s
For every i in 1..n do
Schedule job i from s(i)=f to f(i)=f+ti
f=f+ti i j
What is the idle time and max # inversion for greedy schedule?