I think prof Hsu is a great professor! The homeworks, book examples, and lecture worksheets were all very helpful for the two midterms and final. She is not the type of prof to put super difficult material you've never seen before on the exams. I didn't love the true/false and multiple choice on the exams, but some were easy points. Also if you're taking this online she always posted her office hour recordings and pdfs and I really appreciated it because she went over hw problems in OH.

Also, I didn't always understand the material just based off her lectures , so I would recommend using YouTube, specifically professor Leonard, patrickJMT, and organic chemistry tutor. These YouTube channels really helped me to master the material

Do take this class if you really want to learn! Professor Hsu is amazing; she really has an extensive knowledge base for this course and manipulates this knowledge in the most intelligent of ways. It may be a little hard to keep up at first because the methods she uses to solve problems challenges us to think outside of the box but it is so worth it and eye-opening if you are into learning how to learn. Also-- she is very helpful during class and will pause to answer any questions in chat! HW is long in length but necessary to understand the material; as long as you complete the corresponding problems to the lecture before the next lecture, you should be on track in general and prepared for the quizzes. Exams are reasonable, I would just recommend having a qualitative and quantitative understanding since there are T/F and MC questions in addition to those that involve calculation.

Okay, so I was extremely shocked at why I got a B in this class but I'm not complaining. Let's dive into the mechanics of this class (I'm sure most of you that are reading this right now have to take this class as a pre-requisite for your major)
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LECTURES
This is one of those classes where the lectures either work or don't work for you. She tends to focus on the concepts rather than the actual calculations and because of this, she always seems to rush through the material in a short fifty minute period. I can not tell you how many times I've come out of a lecture and was like "What the heck did I just learn?". She usually has a printed out worksheet for all the students, but she also puts them up on CCLE for those who prefer to take notes on their tablets or computers (although she doesn't put them up before every lecture so I recommend just getting one of the hard copies that she prints out for every lecture). The worksheets often contain notes and practice problems which are helpful to learn and understand the concepts.
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GRADING
If you took Math 31A/L, you would understand the general grading scheme. There are two grading schemes that you can use, but the one that is used for you personally is the one that gives you the highest score. The first grading scheme takes both of your midterms into account while the second grading scheme takes the HIGHEST of your two midterms and the final exam is weighted more heavily.
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HOMEWORK
On weeks that you have a quiz, there is homework assigned but you do NOT have to turn in (I'll dive into why you should do your homework even when you don't have to turn it in for credit later). I also find this pattern where she typically assigns a CRAZY amount of homework for the weeks that we have quizzes (I'm very very very salty about that one week where she assigned problems #1-50 on a week we had a quiz). On weeks that you don't have a quiz, you have roughly around 10-15 problems after each lecture that you have to submit before 9 pm on Sunday. Also, your lowest homework score will be dropped.
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QUIZZES
So back to why you should do your homework every week. Remember how I said that on weeks you have a quiz, you don't need to turn in your homework for credit? Well, she pulls questions from those homework problems and quiz you using them. The problems are EXACTLY the same so as long as you did your homework and remember the mechanics to solving those kinds of problems, you'll be fine. She only gives you two problems but it's out of ten points. Screw up one problem, you already got a 50% on that quiz (assuming you get the other problem correct). Also, your lowest quiz score is dropped.
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MIDTERMS
Where do I begin with this one? I hated every single exam she ever gave out. The average on the first midterm was 60%. A lot of people struggled with time management, but on the side, I personally struggled with both time management AND the problems on the midterm. The midterm was insanely difficult and tested us on some concepts that were never covered in class. The average on the second midterm was around 70-80% (can't remember), so there was definitely an improvement. I think she really took our first midterm evaluations seriously and lessened the difficulty and the number of problems on the second midterm. The structure of each midterm is usually as follows: five multiple-choice problems on the first page, followed by four-five short answer questions. There's always partial credit, so try your best to solve them.
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FINAL EXAM
Well, the situation that we had was certainly a unique one. Due to the rest of Winter Quarter 2020 and Finals Week being shifted online, she had to change her entire final exam. Following the structure of her midterms, I'm assuming that she would have also given us multiple choice and short answer questions that fit the general time frame of three hours. Instead, we had twenty multiple-choice questions, with one 12 point extra credit problem that would be added to our first midterm score to increase our score (since everyone scored so low).
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TAs
I sometimes found the TAs more helpful than the actual professor, but I think that's because the TAs work with smaller groups and are able to address more of the students' needs. If you can, go to your TA's office hours (or another TA's) for additional help. I went a few times and my TA was really helpful in helping me clear up some concepts.
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OFFICE HOURS/PROFESSOR'S CHARACTER
I personally didn't go to any of her office hours due to time conflicts, but she set aside about two-three hours for office hours each week. She usually reminds everyone in the beginning of each lecture when she's having office hours which is nice. Talking about her as a person generally, she's a nice professor and knows how to take critique (as demonstrated with how the average of the second midterm increasing). Also, I don't know if she has multiple of the same shirt, but I swear she wears the same shirt to every lecture. I just thought this was something funny I have to point out.
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EXTRA CREDIT
There's a few opportunities for extra credit but it's not much. There is a mid-quarter evaluation (after the first midterm), a final exam question, and the course evaluation that can be completed for some extra credit points.

I like professor Hsu. She's really nice and caring, and I like her positive energy. I wish I had the chance to take her in person. Her class and lectures are very organized. The pacing of the class was good because we were able to cover everything she wanted to from the syllabus, though we did deviate from the syllabus a little since she wanted to talk about Bitcoin $$$. She's alright during lecture, but sometimes I'll get lost since I have no idea what she's talking about. And she's extremely confusing when she's doing a proof. One time she did a proof from the homework during office hours and I copied her proof onto my homework and when my homework got graded, I lost points since there were flaws in the proof. :( Perhaps I would avoid taking a proofs class with her if you can. It helps to read the textbook because it's sometimes better than her notes.
Hsu takes into consideration feedback from the students. We filled out two surveys during the quarter. At first, the workload was a little heavy, but someone complained about the workload on Piazza so the homework assignments gradually got cut down to about 3-5 problems. Most of the problems will come from the textbook. There will be some problems with tedious calculations like calculate 23^3 * 19^5 * 11^4 (mod 97). We're required to do some problems by hand, and some problems using Sage. She'll provide the Sage instructions on the homework but it's usually straightforward. You don't need coding experience to do well in this class. We had 9 homework assignments this quarter (1 homework / week... we had a homework due during finals week :( ). I appreciate that she published the homework solutions to every assignment.
Her exams are straightforward, given the online setting. This is probably my only online math class where I thought all the exams were possible to complete in the suggested time of 1 hour for the midterm and 3 hours for the final. Both of the midterms consisted of about 3 multiple choice questions and 2-3 fill in the blank which are the conceptual questions that I usually would get incorrect. The rest of the exam is mostly 4 computational questions, and 1 proof question. The proof question is alright, and it's easier than the proofs from the homeworks. The averages on the midterms were in the 90s, which is to be expected since the questions were mostly computational. I would imagine the exams to be harder in person since there's a lot of algorithms to memorize and I don't know if she'll let you use your notes. The algorithms aren't hard to perform, but it might be hard to memorize all the steps. I scored well on the exams but I think I would get a much lower score if I had to take the exams in person because I would not remember all the algorithms and cryptosystems. If you are good at memorization, then you will do well when taking the in-person exams.
I don't think it's absolutely necessary to have taken 115a before this class. We did a section on lattices which did involve linear algebra, but if you have taken 33a, you should be fine. However, I think you should have some exposure to proofs. Some homeworks will have 1-3 proofs in it, and you should expect a proof on the exams. Also maybe it could help to have exposure to algebra (110a) but it's not necessary since this class doesn't assume any algebra knowledge. I haven't taken 110a and I still did well. You should expect to do lots of modular arithmetic in this class. At times, this class felt more like a number theory/algebra class than a cryptography class. This class makes me bored sometimes but I would recommend this class if you have some interest in cryptography.

I took Professor Hsu for 31A in Fall 2019, and she has undoubtedly bettered herself this Quarter for Math 31B and I loved her for how she made a point to learn from her evaluations whether from Fall or in Winter and better herself accordingly. Her Exams this Quarter were extremely simple. I am not great at Math, but I could complete her Midterm 1 in 35 minutes, and 2 in 20 minutes. For her Exams, solve each and every problem type, if not each and every problem.
Quizzes were also extremely simple and were from the questions she had assigned, no surprises, however, she assigned a large number of questions and that could be strenuous. The Homework was also problematic in that manner. Also, she added exercises in her syllabus that the other Math 31B Professor didn't do. In that sense, this Class can be intensive but it is extremely doable.
I will definitely recommend Professor Hsu if you are interested in learning. The level of easiness or difficulty in this Class depends on how much work you are willing to do outside her class. Do not let other reviews mislead you.

Professor Hsu is one of the most brilliant math professors I have ever been taught by. Her lectures are incredibly organized, and she gives out these comprehensive sheets every class that effectively summarizes the topic covered in that class. Her homework questions are very simple to do if one revises their class notes and reads that section from the textbook. The homework also helps you gain a better grasp of the different types of sums that can be asked from that section. Her midterms had pretty standard math sums of similar difficulty to that of the homework. She, however, asks a bunch of True or False questions in her midterm and final which are very technical in nature and are worth a lot of points (so remember to learn your theorems and understand your concepts well). Her midterms are definitely lengthy but are pretty possible to finish as long as you don't get stuck on something for too long. Her final, however, was considerably much easier and much more lenient time-wise. Her office hours are extremely helpful only if you have questions that need to be answered and she is very helpful in answering doubts and clearing concepts. She is very approachable and makes an effort to remember your names.
Tip: Something that really helped me with the homework for this class is forming an intimate study group of 2 or more people with whom you discuss the homework on Thursday (as every homework assignment is due on Friday). It helps ensure that you have all the right answers if you were not able to make it to office hours and ensures you finish the homework a day early instead of rushing to finish it later. Homework is worth a good portion of your grade, and it is very easy to mess up so be careful.

Dr. Hsu is a great teacher. She knows her things and teaches well and is extremely helpful. She provides Assignments in each and every Class which has the Theory and Questions on the Topic she will be teaching in that specific Class. Homework Questions are easy and doable. However, neither of them will prepare you for her Exams especially the True and False Questions which have an unnecessarily high percentage of marks. For Math 31A (Fall 2019), she tested us on Sections 6.3 and 6.4 which were not tested in other Math 31A Classes which made studying and the Exam more difficult. If you are a person who can do well or even just sail through the Exams, I will highly recommend Dr. Hsu.

I took this class fall quarter of my freshman year. It was 4 days a week at 8 am, a freaking nightmare. Anyway, Dr. Hsu was a good professor and I understood the material taught in class. However, maybe that was due to the fact that I had already covered most of the topics of this course in high school with top grades, but couldn't transfer credits so couldn't skip the class (I am international). Her midterms weren't too hard, but very long. You have to go very fast or you won't finish them. Instead, I had plenty of time on the final. Also, the problems on the tests were usually not the hardest kinds that we did in class. For example, for volumes of revolution, instead of having area between curves rotated around a random axis y or x = k, we only had to compute the volume of the sphere around whatever axis we wanted. That was very nice. Homework is not heavy, but sometimes she assigns super hard problems that not even the TAs can do on the spot. To solve those, go to office hours, they are super helpful and she gives out homework solutions. Homework is graded, so that's basically free points. no participation grade for this class. The TA Erza Thompson is super boring. Overall, my experience with this professor was good, also because of my grade. Consequently, I chose her again for Math 31B.

She's a great teacher. Only criticism is that the exams are pretty difficult. Prepare for true/false. I know.

I'll try to give a review without bursting out in anger and get all biased haha.
Her teaching style is really not for everyone. Honestly from what I have heard and seen from the students who took 31B with her was that you either understand what she is teaching or you don't. For me, I struggled HARD, and I had to teach myself the course all on my own. After the monstrosity of midterm 1 I stopped going to lectures (don't worry they were bruincasted). Her exams can be unpredictable and sometimes you won't even have enough time to do all of the problems. How she teaches the class may be very difficult to adapt to because she heavily focuses on the concepts and derivations of formulas and whatnot, instead of calculations. From the lectures I actually went to, she expects students to easily understand the lesson content and that may be why some students became frustrated with her because she sometimes does not slow down or fully explain what she is writing.
My best advice to truly do well in her class: after lecture, start doing the assigned homework problems so that you don't fall behind. on the textbook, go through what the textbook teaches you (to help you solidify the material) and then do the homework problems.
In my opinion, the TAs teach you better and give you more ways to do problems that will actually help you understand. I believe that a lot of people started to trust their TAs more than Hsu herself.
In a sense, Hsu does care for her students. She encourages students to go to her office hours if they were confused with the lecture material. She'll ask for feedback on the exams and she tries to adjust the exam material that fits the general strengths of her students. I believe that this quarter was the first time she has taught 31B, so I am sure she will adjust her course.
31B was all new material to me and I just did not like how she taught the class, but her method works for others. If you plan to take Professor Hsu in the future, I wish you luck.