CS 3100

Data Structures and Algorithms 2

Announcements, Spring 2025

Aaron Bloomfield (aaron@virginia.edu)
Raymond Pettit (raymond.pettit@virginia.edu)
@github | ↑ |

Final Exam

For those of you also taking Game Theory, your grade in that class will be based on how close your grade on this exam is to 80% of the average.

xkcd # 2385

Lecture 29: Tuesday, April 29th

Assignments
- PA5, on reductions, is due today, Tuesday, April 29th (the last day of classes)
Quizzes 3&4 are graded and returned
- Quiz 3 average was 86.1, quiz 4: average was 62.5
- There was some grade modifications to bring the two sections into balance
- Regrades will open up later today
Grading:
- Grades returned through PS6
- We are now working on PS7+
- PA grades, and auto-grader fixes, will be happening over the next week or so
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Final exam: this Friday from 7-10pm
- In Gilmer 301 (for Bloomfield’s 9:30 am section) and Gilmer 390 (for Pettit’s 2 pm section)
- PS solutions through PS9, and quiz 5 from last semester, are on Canvas’ Files
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
  - TA OH follow the regular schedule today; TA OH are 5-7 Wed and Thu of this week
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Today we will work through a course conclusion and a review session

Machine Learning

The pile gets soaked with data and starts to get mushy over time, so it's technically recurrent.

xkcd # 1838

Lecture 28: Thursday, April 24th

Assignments
- PS10 was due yesterday
- PA5, on reductions, is out; due Tuesday, April 29th (the last day of classes)
Quizzes 3&4 last Thursday
- It’s currently 88% graded
Grading:
- Grades returned through PS6
- PA2 auto-grader concerns are yet to be dealt with
- PA3 grades returned on Saturday (March 29th); please post auto-grader concerns on Piazza post @220
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we will continue with machine learning

NP-Complete

xkcd # 287

Lecture 27: Tuesday, April 22nd

Assignments
- PS10 is due tomorrow, Wednesday, April 23rd
- PA4, on DP was due last Friday; how was it?
- PA5, on reductions, is out; due Tuesday, April 29th (the last day of classes)
Quizzes 3&4 last Thursday
- It’s currently 83% graded
Grading:
- Grades returned through PS6
- PA2 auto-grader concerns are yet to be dealt with
- PA3 grades returned on Saturday (March 29th); please post auto-grader concerns on Piazza post @220
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we will finish with Reductions (slides also in Canvas’ Files)
- Next up: machine learning

Here to Help

"We TOLD you it was hard." "Yeah, but now that I'VE tried, we KNOW it's hard."

xkcd # 1831

Lecture 26: Thursday, April 17th

Assignments
- PS9 was due yesterday (April 16th)
- PS10 will be out late this week, is due Wednesday, April 23rd
- PA4, on DP, is out; due this Friday (April 18th)
- PA5, on reductions, is out; due Tuesday, April 29th (the last day of classes)
Quizzes 3&4 last Thursday
- It’s currently 78% graded
Grading:
- Grades returned through PS6
- PA2 auto-grader concerns are yet to be dealt with
- PA3 grades returned on Saturday (March 29th); please post auto-grader concerns on Piazza post @220
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we will continue with Reductions (slides also in Canvas’ Files)

Coordinate Plane Closure

3D graphs that don't contact the plane in the closure area may proceed as scheduled, but be alert for possible collisions with 2D graph lines that reach the hole and unexpectedly enter 3D space.

xkcd # 2735

Lecture 25: Tuesday, April 15th

Assignments
- PS9 is out and due Wednesday (April 16th)
- PA4, on DP, is out; due this Friday (April 18th)
- PS10 will be due next Wednesday, April 22nd
- PA5 will be due Tue, April 28th (the last day of classes)
Quizzes 3&4 last Thursday
- It’s currently 77% graded
Grading:
- Grades returned through PS6
- PA2 auto-grader concerns are yet to be dealt with
- PA3 grades returned on Saturday (March 29th); please post auto-grader concerns on Piazza post @220
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we will continue with Reductions (slides also in Canvas’ Files)

Wisdom of the Ancients

All long help threads should have a sticky globally-editable post at the top saying 'DEAR PEOPLE FROM THE FUTURE: Here's what we've figured out so far ...'

xkcd # 979

Lecture 23: Tuesday, April 8th

Assignments
- PS9 due next week, so will be released late this week
- PA4, on DP, is out; due date April 18th
- PS9 and PS10 will be due April 15th & 22nd, respectively
- PA5 will be due Tue, April 28th (the last day of classes)
Quizzes 3&4 this Thursday (4/10)
- Sample quizzes and topic coverage are available in Canvas’ Files
Grading:
- Grades returned through PS5
- All PA1 auto-grader concerns on Piazza have been handled
- PA2 auto-grader concerns are up next to be dealt with
- PA3 grades returned on Saturday (March 29th); please post auto-grader concerns on Piazza post @220
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we will continue with Reductions (slides also in Canvas’ Files)

Tech Support Cheat Sheet

'Hey Megan, it's your father. How do I print out a flowchart?'

xkcd # 627

Lecture 22: Thursday, April 3rd

Assignments
- PS8 was due yesterday
- PS9 due the week after next, so will be released next week
- PA4, on DP, is out; due date April 18th
- PS9 and PS10 will be due April 15th & 22nd, respectively
- PA5 will be due Tue, April 28th (the last day of classes)
Quizzes 3&4 next Thursday (4/10)
- We’ll release a sample quiz and topic coverage late this week, as well as solutions through PS7
Grading:
- PS5 grades were returned yesterday (March 31st)
- All PA1 auto-grader concerns on Piazza have been handled
- PA2 auto-grader concerns are up next to be dealt with
- PA3 grades returned on Saturday (March 29th); please post auto-grader concerns on Piazza post @220
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we will continue with Reductions (slides also in Canvas’ Files)

Travelling Salesman Problem

What's the complexity class of the best linear programming cutting-plane techniques? I couldn't find it anywhere. Man, the Garfield guy doesn't have these problems ...

xkcd # 399

Lecture 21: Tuesday, April 1st

Assignments
- PS8 is out and due tomorrow (April 2nd)
- PA4, on DP, is out; due date April 18th
- PS9 and PS10 will be due April 15th & 22nd, respectively
- PA5 will be due Tue, April 28th (the last day of classes)
Quizzes 3&4 next Thursday (4/10)
- We’ll release a sample quiz and topic coverage late this week
Grading:
- PS5 grades were returned yesterday (March 31st)
- All PA1 auto-grader concerns on Piazza have been handled
- PA2 auto-grader concerns are up next to be dealt with
- PA3 grades returned on Saturday (March 29th); please post auto-grader concerns on Piazza post @220
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we will finish with Dynamic Programming; slides are in Canvas’ files
- Next up: Reductions (slides also in Canvas’ Files)

Tree

Not only is that terrible in general, but you just KNOW Billy's going to open the root present first, and then everyone will have to wait while the heap is rebuilt.

xkcd # 835

Lecture 20: Thursday, March 27th

Assignments
- PS7 was due yesterday – how did it go?
- PA4, on DP, is out; due date TBA
- PS8 will be out late this week
Quizzes 1&2 last week were returned last week
- See Prof. Pettit’s announcement from Tuesday, 3/18
- Regrades open until this weekend
Grading: grades returned through PS4
- Grades for PA1 and PA2 returned; there are unhandled concerns that will be addressed (see Piazza posts @191 and @192); this will take some time
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change); but none for me on Monday
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
We’ll talk about some anonymous feedback today
Today we will continue with Dynamic Programming; slides are in Canvas’ files

Watson Medical Algorithm

Due to a minor glitch, 'discharge patient' does not cause the algorithm to exit, but instead leads back to 'hunt down and capture patient'.

xkcd # 1619

Lecture 19: Tuesday, March 25th

Assignments
- PS7, on DP, is due tomorrow
- PA3 was due last Friday – how did it go?
- PA4, on DP, is out; due date TBA
Quizzes 1&2 last week were returned last week
- See Prof. Pettit’s announcement from Tuesday, 3/18
- Regrades open for one week
Grading: grades returned through PS4
- Grades for PA1 and PA2 returned; there are unhandled concerns that will be addressed (see Piazza posts @191 and @192); this will take some time
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we continue will continue with Dynamic Programming
- The slides are in Canvas’ files

Complexity Analysis

PERPETUALLY OPTIMISTIC CASE: Early in the execution, our research group makes a breakthrough on proving P=NP.

xkcd # 2939

Lecture 18: Thursday, March 20th

Assignments
- PS6 was due yesterday – how was it?
- PS7 will be out tomorrow, due next Wednesday
- PA3 is out, due tomorrow (Friday)
- PA4 will be out this weekend
Quizzes 1&2 last week were returned
- See Prof. Pettit’s announcement from Tuesday
- We’ll talk a bit about the curve, regrades, etc; regrades will open later today
Grading: grades returned through PS4
- Grades for PA1 and PA2 returned; there are unhandled concerns that will be addressed (see Piazza posts @191 and @192); this will take some time
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we continue will continue with Dynamic Programming
- The slides are in Canvas’ files

Ineffective Sorts

StackSort connects to StackOverflow, searches for 'sort a list', and downloads and runs code snippets until the list is sorted.

xkcd # 1185

Lecture 17: Tuesday, March 18th

Assignments
- PS6 is due tomorrow
- PS7 will be out late this week
- PA3 is out, due this Friday
- PA4 will be out (hopefully) late this week
Quizzes 1&2 last week: will be returned today
- We will go over them on Thursday, at which point regrades will open
Grading
- Grades returned through PS4
- Grades for PA1 and PA2 returned; READ THE PA1/PA2 DISCLAIMER ON PIAZZA!
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 2-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we continue will finish Greedy algorithms, and start on Dynamic Programming
- The slides are in Canvas’ files

Python

xkcd # 353

Lecture 16: Thursday, March 6th

Assignments
- PS5 was due yesterday – how did it go?
- PA2 is out, and due this Friday
- PA3 is out, due two weeks from this Friday; submission opens up this Saturday
- PS6 will be out late this week, due the Wednesday after spring break; also on Greedy algorithms
Quizzes 1&2 last week: should be returned tomorrow
- We will go over them after spring break, at which point regrades will open
Grading
- PS1 through PS3 have been returned; PA1 is delayed, and PS4 is being graded
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 1:30-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
- None over spring break
Course textbook link is on the Canvas landing page
Today we continue with Greedy algorithms
- The slides are in Canvas’ files

Lecture 15: Tuesday, March 4th

Assignments
- PA2 is out, and due this Friday
- PA3 will be out late this week, due the Friday after spring break; on Greedy algorithms
- PS5 is out, due this Wednesday; on Greedy algorithms
- PS6 will be out late this week, due the Wednesday after spring break; also on Greedy algorithms
Quizzes 1&2 last week: how were they?
Grading
- PS1 through PS3 have been returned; PA1 is delayed, and PS4 is being graded
- Midterms should be back late this week
- For PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
- Prof Bloomfield: M 10-11:30, W 1:30-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we continue with Greedy algorithms
- The slides are in Canvas’ files

Tuesday, February 25th: Warm-up

Imagine a world without computerized cash registers!

The problem: Given unlimited quantities of pennies, nickles, dimes, and quarters (worth 1, 5, 10, and 25 cents, respectively), design an algorithm to determine a set of coins (the change) for a given value \(x\) using the fewest number of coins.

Tuesday, February 25th

Assignments
- PA2 is out, and due a week from Friday
- PS5 will be out late this week, due next Wednesday; on Greedy algorithms
Grading
- PS3 has been returned, PA1 should be back this weekend
- for PS assignments, regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Quizzes 1&2 are this Thursday
- Topic list and past quizzes are in Canvas’ Files
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Rice 109
  - No TA office hours this Thursday
- Prof Bloomfield: M 10-11:30, W 1:30-3 in Rice 402 (note the change)
  - But not this Wednesday
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we start on Greedy algorithms
- The slides are in Canvas’ files

Tuesday, February 18th

Assignments
- PS4 is out and due tomorrow
  - Yes, some answers are in the LaTeX file – you can use them, but you still need to understand the problems!
- PS5 will be due the week after quizzes 1&2
- PA1 was due Saturday – how was it?
- PA2 will be out by Thursday, due on Friday in 2.5 weeks
Grades through PS2 have been returned
- Regrade requests need to be submitted, via Gradescope, within a week of when it was returned
Quizzes 1&2 are next Thursday; more info this Thursday
Office hours:
- TA OH in Rice 109: Sun 5-7 and M/Tu/W/Th from 5-9 in Olsson 009
- Prof Bloomfield: M 10-11:30, W 1:30-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we continue with divide and conquer, which we will wrap up on Thursday
- The slides are in Canvas’ files

Thursday, February 13th

PS3 is was due yesterday – how was it?
PS4 will be out late this week
PA1 is out, due ~~Friday~~ Saturday, Feb 15th
- It’s on Dijkstra’s shorted path algorithm
- Submission is open, but will be unavailable Friday night into Saturday morning
Grading:
- PS0 and PS1 are graded and returned
- PS2 is being graded (99% completed)
Office hours:
- TA office hours are now in Rice 109
- TA OH: M/Tu/W/Th from 5-9 in Olsson 009
- Prof Bloomfield: M 10-11:30, W 1:30-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Tuesday was a snow day; there was a video to watch on Canvas
- Topics covered: finishing of Karatsuba multiplication, and guess-and-check
Today we continue with divide and conquer, which will take 4-5 lectures
- The slides are in Canvas’ files

Tuesday, February 11th

Today was a UVA snow day, and there was a video to watch via Canvas

Warm-up (Feb 6)

Can you cover an 8x8 grid with 1 square missing using “trominoes”?

Tromino:

https://nstarr.people.amherst.edu/trom/puzzle-8by8/

Thursday, February 6th

PS2 is was due yesterday – how was it?
PS3 will be out late this week
PA1 is out
- It’s on Dijkstra’s shorted path algorithm
- Due date is Friday, February 14th
- The submission will be up in a day or two
Grading:
- PS0 is graded and returned
- PS1 is being graded (85% completed)
- PS2 is going out to be graded today
Office hours:
- TA office hours are now in Rice 109
- TA OH: M/Tu/W/Th from 5-9 in Olsson 009
- Prof Bloomfield: M 10-11:30, W 1:30-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we start on divide and conquer, which will take 4-5 lectures
- The slides are in Canvas’ files

Tuesday, February 4th

PS2 is due tomorrow
PA1 is out
- It’s on Dijkstra’s shorted path algorithm
- Due date is Friday, February 14th
Office hours:
- TA office hours are now in Rice 109
- TA OH: M/Tu/W/Th from 5-9 in Olsson 009
- Prof Bloomfield: M 10-11:30, W 1:30-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we continue (and likely finish) with graphs
- This will take about 5 lectures total
- The slides are in Canvas’ files

Thursday, January 30th

PS1 was due yesterday
PS2 will be out today, due next Wednesday
PA1 will be out today
- It’s on Dijkstra’s shorted path algorithm; we’ll go over it today
- Due date not yet set, but likely the week after next
Office hours:
- TA office hours are moving to Rice 109
- TA OH: M/Tu/W/Th from 5-9 in Olsson 009
- Prof Bloomfield: M 10-11:30, W 1:30-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we continue with graphs
- This will take about 4 5 lectures total
- The slides are in Canvas’ files

Tuesday, January 28th

PS1 will is due tomorrow by midnight
PS2 will be out late this week
PA1 is almost ready
- It’s on Dijkstra’s shorted path algorithm
Office hours:
- TA OH: M/Tu/W/Th from 5-9 in Olsson 009
  - We may add a Sunday shift
- Prof Bloomfield: M 10-11:30, W 1:30-3 in Rice 402 (note the change)
- Prof Pettit: M 2:30-4:00, F 1:30-3:00 in Rice 212
Course textbook link is on the Canvas landing page
Today we continue with graphs
- This will take about 4 lectures total
- The slides are in Canvas’ files

Thursday, January 23rd

PS0 was due yesterday
PS1 will be out today, due next Wednesday by midnight
Office hours:
- TA OH: M/Tu/W/Th from 5-9 in Olsson 009
  - We may add a Sunday shift
- Prof Bloomfield: M 9:30-11, W 1:30-3 in Rice 402 (note the change)
- Prof Pettit: TBA in Rice 212
Course textbook link is on the Canvas landing page
Today we continue with graphs
- This will take about 4 lectures total
- The slides are in Canvas’ files

Tuesday, January 21st

PS0 is due tomorrow (Wednesday, Jan 22) by 11:59 pm
- It’s in Canvas’ assignments
- Submit via Gradescope
PS1 will be out late this week, due Wednesday of next week
Office hours:
- TA OH: M/Tu/W/Th from 5-9 in Olsson 009
  - We may add a Sunday shift
- Prof Bloomfield: M 9-11, W 2-3 in Rice 402
- Prof Pettit: TBA in Rice 212
Course textbook link is on the Canvas landing page
Today we start graphs
- This will take about 4 lectures
- The slides are in Canvas’ files

Thursday, January 16th

PS0 (out today) due next Wednesday (Jan 22) by 11:59 pm
- It will be in Canvas’ Assignments
PS1 out next week, due the following Wednesday
Course textbook link is on the Canvas landing page
TA office hours coming soon (we are targeting Sun-Thu, 5pm-9pm)
Prof. Bloomfield office hours TBA
Prof. Pettit office hours TBA