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CO 342Introduction to Graph Theory

Units
0.50
Faculty
Mathematics
Subject
Combinatorics and Optimization

When it runs

  1. F24
  2. W25
  3. S25
  4. F25
  5. W26
  6. S26
  7. F26
  8. W27
  9. S27

Ran in 5 of the last 7 terms. Winter 2027: not on the schedule. Spring 2027: schedule not out yet.

An introduction to some of the key topics in graph theory: connectivity, planarity, and matchings. Connectivity: Menger's theorem, 3-connected graphs. Planarity: Kuratowski's theorem, uniqueness of planar embeddings. Matchings: Review of Konig's theorem, Tutte's theorem.

Prerequisites

  • Must have completed at least 1 of the following:
    • MATH239 - Introduction to Combinatorics (0.50)
    • MATH249 - Introduction to Combinatorics (Advanced Level) (0.50)

Antirequisites

None listed.

Leads to

Fall 2026 sections

Enrolment from UW Open Data, which can trail Quest by up to two days. Instructors and rooms: Schedule of Classes.
SectionClassEnrolledMeets
LEC 001595355 / 80TTh 10:00–11:20

Resources

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Reviewed on UW Flow

89% liked it30% easy74% useful

From 63 ratings and 19 comments on UW Flow. The most helpful comments, quoted as written, without names. Read them all on UW Flow.

  • Very difficult course with Martin Pei. Along with a straightforward lecture review, we had three weekly, difficult, rigorous proof questions. Despite starting as early as possible for majority of these questions, I would be working on them for most of the day, every day up until the due date and still not be able to fully finish one or two. While Martin Pei's lectures were superb (as usual), they almost never provide any direction whatsoever for any of the proof questions. Rather, they state a basic definition or a key theorem we need to use *somewhere* in the proof. Many of the proof questions require a lot of creative thinking, to the point where reading the posted solutions is…

    Aug 2021 · didn’t like it · 3 found this helpfulOn UW FlowRemove this

  • Fun and interesting but also dragged me through all 9 levels of hell
    class was split into normal students and prodigies, one half of the class would be getting 50% on assignments and tests and the other half be getting perfect

    Aug 2023 · liked it · 1 found this helpfulOn UW FlowRemove this

  • A very well structured course (lemma -> proof -> theorem -> proof -> corollary -> *picture of some concrete example* -> repeat). At one point I realized that my brain didn't evolve to think about graphs. But it was a fun course. Also, whoever invented Tutte theorem should stop being so hardcore. Oh right, it was invented by Tutte.

    Dec 2017 · liked it · 1 found this helpfulOn UW FlowRemove this

  • A very fun and structured course. Prof. Haxell was a great lecturer and very clear and explaining concepts. Quizzes and assignments were very well structured to help us learn the content, and I felt like I was actively absorbing content throughout the term. Exams were weighted a bit high and everything was marked pretty harshly, so grades were a bit on the lower side (need to work very hard for a 90), but overall a great and fun course!

    Jan 2026 · liked itOn UW FlowRemove this

  • Somewhat hard but very fun and well-structured. weekly-ish assignments (2 questions, lowest 2 dropped), weekly-ish quizzes (1 question, variant of question from that week's assignment, lowest 2 dropped), and weekly simple learn quizzes (lowest 2 dropped). The content itself was really fun if you like graph theory, and the structure (for Haxell's offering) really helped to not only understand the content, but also build inution for them as well. Would gladly take again.

    Dec 2025 · liked itOn UW FlowRemove this

Discussed on r/uwaterloo

139 posts and comments in 111 threads mention CO 342, December 2011 to December 2024. Quoted word for word, newest first; each reply sits under the post and the comment that started its branch. Search r/uwaterloo for newer posts.

Fall 2024

CO342 2 points, 2 comments

u/SpiritedTie9025: “Hi guys, I am having a heavy course load this term, (CS246 + CS245 + CO456 + CO342), and I find that I don't have too much time on CO342. I wonder if this course really need time to comprehend and practice (since it's been only 2 weeks on this course so I can't really feel it). …”

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Spring 2024

PMATH 347 After MATH 235 7 points, 4 comments

“I’m interested in taking this course after having taken Math 235. Yu-ru is teaching it this Fall which I’ve heard is an easier offering than usual. …”

u/AHpache182: “… Regardless, PMATH 347 is the hardest course I've taken to date (on par with CO 342). …”

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Spring 2023

3B Course Load 1 point, 0 comments

u/Zealousideal_Goat424: “I'm currently taking CS350, CO351, PMATH 347, STAT 341. I'm thinking about adding CO 342, but it's currently full, and the other courses are looking heavy. Should I just roll with 4 courses? Or go for graph theory (co342) if it opens up?”

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Most Recommended CO Courses? 22 points, 21 comments

“What are your most recommended CO courses regardless of hardness? :D Thank you\”

u/not_a_rhymer: “… To my knowledge it's offered this summer, so have fun My second recommendation is CO342: Intro to Graph Theory. I had with with Dr. Spirkl last summer. This was a MUCH tougher course than CO351 and probably up there with the hardest CO courses I've personally taken. …”

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Winter 2023

Martin pei, you deserve better students. 608 points, 47 comments

“Man, he shows up every lecture excited to teach, and only like a 10th of the class shows up. There was 9 of us today in a class of like 70 ish students or something, and same on Monday. …”

u/-Void-: “He is the best! I had him for CO 456 and CO 342, and his lectures were always on point and he was always super helpful and friendly during office hours. He also gives great advice :3”

u/GooseGoneRogue: “I had him for CO 342 and can confidently say that he’s the only professor that had me considering grad school at all. I remember at the time he mentioned that he took classes on a contractual basis and it’s a real shame that he isn’t on tenure track already. …”

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CO454 vs CO367 vs CO353 2 points, 8 comments

u/OrangeMint1-2: “… I also plan to take CO 342 in the future, which seems to be the least challenging course among my options. I can take CO 454 next term, CO 367 by changing my co-op sequence, or CO 353 one year later. I have no idea who will teach. …”

u/ribbonkitty: “I took CO 342 last term and am taking CO 353 this term. Personally, I found CO 342 to be fairly challenging but on hindsight, it really improved my understanding of graph theory and how to approach proofs about graphs - it's definitely not a course to be trifled with though. …”

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Fall 2022

What should I do to get approval of 7 courses? 2 points, 35 comments

“Hi everyone. I'm in the Faculty of Mathematics -- and I'm aiming to take 7 courses at some point (it's something like 6 math and 1 elective) from 3A onwards. …”

u/djao: “The actual answer is here: https://www.reddit.com/r/uwaterloo/comments/n62nf0/whataretherequirementstotake6or7courses/ Source: I am on the S&P committee. …”

u/Novel_Brain9700: “Can I ask how does this work? Does this mean taking CO 330 & CO 342 (Enumeration and Graph Theory) implies that you won't need MATH 249? (Suppose that one has taken 330 and 342 before 249 due to overriding)”

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UW Math Major Declaration 4 points, 8 comments

u/No_Inspector_8321: “… &x200B; Table 1 + the following CS 371 Math 237 Math 239 CO 250 CO 342 CO 351 CO367 CO456 PMATH 336 PMATH331 PMATH332 STAT330 STAT331 STAT332 STAT333 STAT440 STAT437 STAT340 STAT442 AMATH250 MTHEL 300 CS371 CS230 CS234 AMATH250 ECON 212”

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