CS 3100

Data Structures and Algorithms 2

Announcements, Spring 2026

Mark Floryan (mrf8t@virginia.edu)
Aaron Bloomfield (aaron@virginia.edu)
@github | ↑ |

Machine Learning

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

xkcd # 1838

Lecture 20: Thursday, March 26th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, but not today (Thu, 3/19)
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203
Assignments
- Nothing due this week; PS7 (DP I) and PA4 (DP) will be out later this week
Grades
- Grades through PS4 and PA1 have been returned
- We expect PA2, PA3, and PS5 to be back by next Tuesday
Regrade concerns?
- If it’s a PA, then via the dedicated Piazza post
- If it’s a PS, then submit it through Gradescope within one week
CBTF for quiz 3
- We do not want the early sessions to have a disadvantage, so we are providing more (see last Tuesday’s slide)
- We will debrief and get feedback on Tuesday
Course textbook link is on the Canvas landing page
Today we will continue with dynamic programming

Genetic Algorithms

Just make sure you don't have it maximize instead of minimize.

xkcd # 534

Lecture 19: Tuesday, March 24th (1/2)

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, but not today (Thu, 3/19)
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203
Assignments
- Nothing due this week; PS7 (DP I) and PA4 (DP) will be out later this week
Grades
- Grades through PS4 and PA1 have been returned
- We expect PA2 to be back this week
Regrade concerns?
- If it’s a PA, then via the dedicated Piazza post
- If it’s a PS, then submit it through Gradescope within one week
CBTF
- Most people took the practice quiz
- Quiz 3 sign-ups are available; see Piazza post @125
- We do not want the early sessions to have a disadvantage, so we are providing more info on the next slide
Course textbook link is on the Canvas landing page
Today we will continue with dynamic programming

Quiz 3 format

The questions on quiz 3 are:

Perform Dijkstra’s shortest path
- Hint: create a table like on slide 14 of the 03-2-DijkstraAndPrim.pdf slide set
Find an MST in a graph (either Kruskal’s or Prim’s)
- A note about scratch paper: copy the NODES only, and the fill in the edges in the MST
Proofs:
- Prove optimal substructure of one of the algorithms we have seen (randomly chosen)
- Prove the greedy choice property of one of the algorithms we have seen (randomly chosen)
- This will be by proof blocks (given a number of steps of the proof, including incorrect steps, select the correct ones and assemble them in the correct order)
- 6 possible algorithms: coin change, Dijkstra’s, MST (both Prim’s and Kruskal’s), activity selection, fractional knapsack
Some number (5-10) of true/false questions from a very large question bank

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 18: Thursday, March 19th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, but not today (Thu, 3/19)
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203
Assignments
- PS6 (greedy II) was due yesterday; how did it go?
- PA3 (greedy) is out, due this Friday (March 20th)
- No PA7 (DP I) released this week, because next week is quiz 3
- PA4 (DP) is due in 3 weeks, so will be out next week
Grades
- Grades through PS4 and PA1 have been returned
- We expect PA2 to be back this week
Regrade concerns?
- If it’s a PA, then via the dedicated Piazza post
- If it’s a PS, then submit it through Gradescope within one week
CBTF
- Wednesday’s practice quiz sessions: a complete failure
- Thursday’s practice quiz sessions: it (almost) worked
- On Friday we will release, on Piazza, info about next week’s quiz 3
  - We are waiting until the practice quiz finishes
Course textbook link is on the Canvas landing page
Today we will continue with dynamic programming

Recipes

To be fair, the braised and confused newt on a bed of crushed Doritos turned out to be delicious.

xkcd # 720

Lecture 17: Thursday, March 16th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203
Assignments
- PS6 is out, and due tomorrow
- PA3 is out, due this Friday (March 20th)
Quizzes 1&2
- They are graded and returned; see Piazza post @88 about a small curve to make up for the typo
- Beyond that, we are not expecting to curve the examns
- Regrades are open for about a week
Grades
- Grades through PS4 and PA1 have been returned
- We expect PA2 to be back this week
Regrade concerns?
- If it’s a PA, then via the dedicated Piazza post
- If it’s a PS, then submit it through Gradescope within one week
CBTF: next slide; it’s THIS week
Course textbook link is on the Canvas landing page
Today we will continue with greedy algorithms

CBTF Info

We will be using a Computer-Based Testing Facility (CBTF) for the rest of the exams in this course
There is a practice exam this week (March 17-19)
- Everybody has to take it!
- We are going to “grade” it to practice the auto-grading, but as long as you complete it, you will get full credit (counts as a homework)
  - It is a 50 minute slot, taken in Gilmer 490A
To register for a slot, see Piazza post @95
- As of last night, only 20% of the class has registered
- If you have a legitimate conflict (out of town, etc.), send an email to the course email
- Otherwise, there will not be a make-up
The current schedule for the practice quiz is:
- Tuesday, 3/17 - 4 pm, 5:30 pm
- Wednesday, 3/18 - 4 pm, 5:30 pm, 7 pm
- Thursday, 3/19 - 2:30 pm, 4 pm, 5:30 pm, 7 pm
The real quiz 3 will be next week
- Wednesday, 3/25 through Friday, 3/27
- Details to follow later this week

AI Hiring Algorithm

So glad Kate over in R&D pushed for using the AlgoMaxAnalyzer to look into this. Hiring her was a great decisio- waaaait.

xkcd # 2237

Lecture 16: Thursday, March 16th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203
Assignments
- PS5 was due yesterday – how did it go?
- PA3 is out, due next Friday (March 20th)
- PS6 will be out today
Quizzes 1&2
- They are graded and returned; see Piazza post @88 about a small curve to make up for the typo
- Beyond that, we are not expecting to curve the examns
- Regrades are open for about a week
Grades
- Grades through PS2 and PA1 have been returned
- We expect PS3, PS4, and PA2 to be back this week
Regrade concerns?
- If it’s a PA, then via the dedicated Piazza post
- If it’s a PS, then submit it through Gradescope within one week
CBTF: next slide; it’s NEXT week, not this week
Course textbook link is on the Canvas landing page
Today we will continue with greedy algorithms

CBTF Info

We will be using a Computer-Based Testing Facility (CBTF) for the rest of the exams in this course
There is a practice exam next week (March 17-19)
- Everybody has to take it!
- We are going to “grade” it to practice the auto-grading, but as long as you complete it, you will get full credit (counts as a homework)
  - It is a 50 minute slot, taken in Gilmer 490A
To register for a slot, see Piazza post @95
The current schedule for the practice quiz is:
- Tuesday, 3/17 - 4 pm, 5:30 pm
- Wednesday, 3/18 - 4 pm, 5:30 pm, 7 pm
- Thursday, 3/19 - 2:30 pm, 4 pm, 5:30 pm, 7 pm
The real quiz 3 will be the following week
- Wednesday, 3/25 through Friday, 3/27

Google Maps

Apparently Google assumes you're traveling during the ferry's normal operating hours. We lost two hours circling that damn lake (to say nothing of the Straw Man).

xkcd # 461

Lecture 15: Tuesday, March 10th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203
Assignments
- PS5 is out, due tomorrow (March 11th)
- PA3 is out, due next Friday (March 20th)
- PS6 will be out on Thursday
Quizzes 1&2
- They are graded and returned
  - See Piazza post @88 about a small curve to make up for the typo
- Beyond that, we are not expecting to curve the examns
- A note about regrades, then they will open up for approximately one week
Grades
- Grades through PS2 and PA1 have been returned
- We expect PS3, PS4, and PA2 to be back this week
Regrade concerns?
- If it’s a PA, then via the dedicated Piazza post
- If it’s a PS, then submit it through Gradescope within one week
CBTF: next slide; it’s NEXT week, not this week
Course textbook link is on the Canvas landing page
Today we will continue with greedy algorithms

CBTF Info

We will be using a Computer-Based Testing Facility (CBTF) for the rest of the exams in this course
There is a practice exam the week after spring break
- Everybody has to take it!
- We are going to “grade” it to practice the auto-grading, but as long as you complete it, you will get full credit (counts as a homework)
It is a 50 minute slot, taken in Gilmer 490A
Login info will be provided right after spring break
The current schedule is:
- 3/17 - 4 pm, 5:30 pm
- 3/18 - 4 pm, 5:30 pm, 7 pm
- 3/19 - 2:30 pm, 4 pm, 5:30 pm, 7 pm
You will be given a link to a system to register for ONE of those sections
Further quizzes in this course will follow a similar pattern
More information about this will be posted in Piazza in the next few days

Tech Support Cheat Sheet

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

xkcd # 627

Lecture 14: Thursday, February 26th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
  - Today: there are OH 5-7, but not 7-9
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
- No OH for some of next week due to exam and the upcoming spring break
Assignments
- PS5 should be out today, due Wednesday after spring break
- PA3 will be out within a week, due three weeks from tomorrow (Fri, Mar 20)
Quizzes 1&2
- They are graded, but…
- There was a problem with the second section, and there may be a statistical discrepancy between the grades; we want to get that sorted out before we return the exams
Grades
- Grades through PS2 and PA1 have been returned
- We expect PS3, PS4, and PA2 to be back right after spring break
Regrade concerns?
- If it’s a PA, then via the dedicated Piazza post
- If it’s a PS, then submit it through Gradescope within one week
CBTF: next slide
Course textbook link is on the Canvas landing page
Today we will continue with greedy algorithms

CBTF Info

We will be using a Computer-Based Testing Facility (CBTF) for the rest of the exams in this course
There is a practice exam the week after spring break
- Everybody has to take it!
- We are going to “grade” it to practice the auto-grading, but as long as you complete it, you will get full credit (counts as a homework)
It is a 50 minute slot, taken in Gilmer 490A
Login info will be provided right after spring break
The current schedule is:
- 3/17 - 4 pm, 5:30 pm
- 3/18 - 4 pm, 5:30 pm, 7 pm
- 3/19 - 2:30 pm, 4 pm, 5:30 pm, 7 pm
You will be given a link to a system to register for ONE of those sections
Further quizzes in this course will follow a similar pattern
More information about this will be posted in Piazza in the next few days

Good Code

You can either hang out in the Android Loop or the HURD loop.

xkcd # 844

Lecture 12: Thursday, February 19th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
- No OH for some of next week due to exam and the upcoming spring break
Assignments
- PS4 was due yesterday – how did it go?
- PA2 is due tomorrow (Friday, Feb 20)
- PS5 will be out next week, due the week after spring break
Grades
- PS0 and PA1 have been returned
- PS1 and PS2 should be back today – then we are caught up!
- PA2 can be graded starting next week
Regrade concerns?
- If it’s a PA, then via the dedicated Piazza post
- If it’s a PS, then submit it through Gradescope within one week
CBTF: we are expecting our first use the week after spring break
- It’s to get used to the system – as long as you complete it, you will not get a penalty
Quizzes 1&2 next Tuesday (Feb 24) in lecture; old quizzes in Canvas’ files
Course textbook link is on the Canvas landing page
Today we will continue with greedy algorithms

Here to Help

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

xkcd # 1831

Lecture 11: Tuesday, February 17th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
- No OH for some of next week due to exam and the upcoming spring break
Assignments
- PS4 is due tomorrow (Feb 18)
- PA2 is due this Friday (Feb 20)
- PS5 will be out next week
Grades
- PS0 and PA1 have been returned
- PS1 should be back today
- PS2 and PS3 should be back next week
- PA2 can be graded starting later this week
Regrade concerns?
- If it’s a PA, then via the dedicated Piazza post
- If it’s a PS, then submit it through Gradescope within one week
Quizzes next Tuesday (Feb 24) in lecture; old quizzes in Canvas’ files
Course textbook link is on the Canvas landing page
Today we will start on greedy algorithms

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 10: Thursday, February 12th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
Assignments
- PS3 was due yesterday – how did it go?
- PA2 is out, due next Friday (Fri, Feb 20th)
- PS4 will be out today, due next Wednesday
Midterms (aka quizzes): there was some confusion on our end about when
- Quizzes 1&2 are Tuesday, February 24th, in lecture (the Tuesday before spring break)
- Quizzes 3&4: we are expecting to move to a CBTF; details to follow
  - If on paper,then they are Thursday, April 9th, in lecture
- Final: Saturday, May 2nd, from 7pm - 10pm
Course textbook link is on the Canvas landing page
Today we will continue with divide and conquer

Flow Charts

At 8 drinks, you switch the torrent from FreeBSD to Microsoft Bob. C'mon, it'll be fun!

xkcd # 518

Lecture 9: Tuesday, February 10th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
Assignments
- PA1 was due last Friday – how did it go?
- PS3 is out, due tomorrow (Wed, Feb 11th)
- PA2 is out, due next Friday (Fri, Feb 20th)
- PS4 will be out Thursday, due next Wednesday
Midterms (aka quizzes): there was some confusion on our end about when
- Quizzes 1&2 are Tuesday, February 24th, in lecture (the Tuesday before spring break)
- Quizzes 3&4: we are expecting to move to a CBTF; details to follow
  - If on paper,then they are Thursday, April 9th, in lecture
- Final: Saturday, May 2nd, from 7pm - 10pm
Course textbook link is on the Canvas landing page
Today we will continue with divide and conquer

Linear Sort

The best case is O(n), and the worst case is that someone checks why.

xkcd # 3026

Lecture 8: Thursday, February 5th

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
- All will be posted on the Canvas landing page
Assignments
- PS2 is due tomorrow
- PA1 is due this Friday
- Upcoming: PS3 will be released today, PA2 released on Friday
Midterms (aka quizzes): there was some confusion on our end about when
- Quizzes 1&2 are Tuesday, February 24th, in lecture (the Tuesday before spring break)
- Quizzes 3&4: we are expecting to move to a CBTF; details to follow
  - If on paper,then they are Thursday, April 9th, in lecture
- Final: Saturday, May 2nd, from 7pm - 10pm
Course textbook link is on the Canvas landing page
Today we will continue with divide and conquer

Dependencies

The prereqs for CPSC 357, the class on package management, are CPSC 432, CPSC 357, and glibc2.5 or later.

xkcd # 754

Lecture 7: Tuesday, February 3rd

Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
- All will be posted on the Canvas landing page
Assignments
- PS1 was due Friday – how did it go?
- PS2 is due tomorrow
- PA1 is due this Friday
- Upcoming: PS3 will be released Thursday, PA2 released on Friday
Midterms (aka quizzes): there was some confusion on our end about when
- Quizzes 1&2 are Tuesday, February 24th, in lecture (the Tuesday before spring break)
- Quizzes 3&4: we are expecting to move to a CBTF; details to follow
  - If on paper,then they are Thursday, April 9th, in lecture
- Final: Saturday, May 2nd, from 7pm - 10pm
Course textbook link is on the Canvas landing page
Today we will continue with divide and conquer

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 6: Thursday, January 29th

PS1 is out and now due this Friday (Jan 30) by midnight
PS2 will be out today, and due next Wednesday (Feb 4) by midnight
- Gradescope submission opens up 72 hours before the due date
PA1 is out, due Fri, Feb 6
- Gradescope submissions are open
Midterms (aka quizzes): there was some confusion on our end about when
- Quizzes 1&2 are Tuesday, February 24th, in lecture (the Tuesday before spring break)
- Quizzes 3&4 are Thursday, April 9th, in lecture
- Final: Saturday, May 2nd, from 7pm - 10pm
- If we use a CBTF, quizzes 3&4 and/or the final may have a different format, time, and location
Course textbook link is on the Canvas landing page
Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
- All will be posted on the Canvas landing page
Today we will continue with graphs

Lecture 5: Tuesday, January 27th

Snow day!

Weird Unicode Math Symbols

U+2A0B ⨋ Mathematicians need to calm down

xkcd # 2606

Lecture 4: Thursday, January 22nd

PS0 was due yesterday – how did it go?
PS1 is out and due next Wednesday (Jan 28) by midnight
- Gradescope submission opens up 72 hours before the due date
- If you don’t see the course, we need to re-sync the roster; email the course email about this
PA1 will be out this Friday, due two weeks later (Feb 6)
Midterms (aka quizzes): there was some confusion on our end about when
- Quizzes 1&2 are Tuesday, February 24th, in lecture (the Tuesday before spring break)
- Quizzes 3&4 are Thursday, April 9th, in lecture
- Final: Saturday, May 2nd, from 7pm - 10pm
- If we use a CBTF, quizzes 3&4 and/or the final may have a different format, time, and location
Course textbook link is on the Canvas landing page
Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
- All will be posted on the Canvas landing page
Today we will continue with graphs

Complexity Analysis

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

xkcd # 2939

Lecture 3: Tuesday, January 20th

PS0 is out in Canvas’ Assignments, and due tomorrow (Wed, Jan 21) by 11:59 pm
- Gradescope submission opens up 72 hours before the due date
- If you don’t see the course, we need to re-sync the roster; email the course email about this
PS1 will be out Thursday afternoon, due next Wednesday (Jan 28)
PA1 will be out this Friday, due two weeks later (Feb 6)
Midterms (aka quizzes): there was some confusion on our end about when
- Quizzes 1&2 are Tuesday, February 24th, in lecture (the Tuesday before spring break)
- Quizzes 3&4 are Thursday, April 9th, in lecture
- Final: Saturday, May 2nd, from 7pm - 10pm
- If we use a CBTF, quizzes 3&4 and/or the final may have a different format, time, and location
Course textbook link is on the Canvas landing page
Office hours
- TA office hours are Mon through Thu, from 5-9 in Rice 442
- Prof. Bloomfield’s office hours Mon 10:30-12 and Thu 12:30-2, in Rice 402, and start this week
- Prof. Floryan’s office hours are Mon 1-2, Tue 9-10, and Wed 12-1 in Rice 203, and start this week
- All will be posted on the Canvas landing page

Algorithms

There was a schism in 2007, when a sect advocating OpenOffice created a fork of Sunday.xlsx and maintained it independently for several months. The efforts to reconcile the conflicting schedules led to the reinvention, within the cells of the spreadsheet, of modern version control.

xkcd # 1667

Lecture 2: Thursday, January 15th

PS0 is out in Canvas’ Assignments, and due next Wednesday (Jan 21) by 11:59 pm
- Gradescope submission opens up 72 hours before the due date
PS1 will be out next week, due the following Wednesday (1/28)
Midterms (aka quizzes): there was some confusion on our end about when
- Quizzes 1&2 are Tuesday, February 24th, in lecture (the Tuesday before spring break)
- Quizzes 3&4 are Thursday, April 9th, in lecture
- Final: Saturday, May 2nd, from 7pm - 10pm
- If we use a CBTF, quizzes 3&4 and/or the final may have a different format, time, and location
Course textbook link is on the Canvas landing page
Office hours
- TA office hours coming soon, and will start next week (we are targeting Mon-Thu, 5pm-9pm); likely in Rice 442
- Prof. Bloomfield’s office hours TBA, in Rice 402, and start next week
- Prof. Floryan’s office hours are TBA, in Rice 203, and start next week
- All will be posted on the Canvas landing page