1. Lecture 40 CSE 331 Dec 8, 2010

2. Finals 3:35-6:05pm KNOX 104 Tue, Dec 14 Blog post on the finals up

3. On Friday, Dec 10 hours-a-thon Atri: 2:00-3:30 (Bell 123) Jeff: 4:00-5:00 (Bell 224) Alex: 5:00-6:30 (Bell 242)

4. Reminder Please fill in the feedback forms from the Engineering school

5. New Grading policy Step 1: Compute grade cut-offs using existing scheme (25% mid term+ 40% finals) Step 2: If 65% finals leads to a better grade for you, I’ll go with the new option

6. Longest path problem Given G, does there exist a simple path of length n-1 ?

7. Longest vs Shortest Paths

8. Two sides of the “same” coin Shortest Path problem Can be solved by a polynomial time algorithm Is there a longest path of length n-1? Given a path can verify in polynomial time if the answer is yes

9. Poly time algo for longest path?

10. P vs NP question P : problems that can be solved by poly time algorithms NP : problems that have polynomial time verifiable witness to optimal solution Is P=NP? Alternate NP definition: Guess witness and verify!

11. Proving P ≠ NP Pick any one problem in NP and show it cannot be solved in poly time Pretty much all known proof techniques provably will not work

12. Proving P = NP Will make cryptography collapse Compute the encryption key! Prove that all problems in NP can be solved by polynomial time algorithms NP NP-complete problems Solving any ONE problem in here in poly time will prove P=NP!

13. Agenda for today A flavor of how NP-completeness works

14. If you are curious for more CSE431: Algorithms CSE 396: Theory of Computation

15. Another course of interest (S 11) CSE 443: Compilers Pre-req: 396 Offered infrequently!