The course staff must critically examine over ten thousand pages of homework submissions this semester! We desperately need your help to make sure homeworks are graded and returned quickly. If you have any questions or concerns about these policies, please don't hesitate to ask in lecture, during office hours, or on Piazza.
We apologize in advance for the length of this document. Most of this stuff is obvious to almost everybody, but after teaching algorithms for a couple of decades, we've seen a lot of strange things.
Homework Logistics: How to submit
- All homework solutions must be submitted electronically via Gradescope. Submit one PDF file for each numbered homework problem. Gradescope will not accept other file formats such as plain text, HTML, LaTeX source, or Microsoft Word (.doc or .docx).
- Each student must submit individual Homework 0 solutions.
- Starting with Homework 1, homework solutions may be submitted by groups of at most three students. We strongly encourage (but will not require) every student to work in a group with at least one other student. Students are are responsible for forming their own homework groups. Groups may be different for each numbered homework problem.
- For group solutions, exactly one member of each group submits the solution to each problem. Even if the groups are identical, the submitter may be different for each numbered homework problem.
- Whoever submits any group solution must also submit the names of the other group members via Gradescope. Gradescope will then automatically apply the grade for that submission to all group members. If this information is not entered correctly, the other group members' grades will be delayed or possibly lost entirely.
- If you discover that your name was omitted from a group homework submission, please submit a regrade request.
- As error correction, each submitted homework solution should include the following information in large friendly letters at the top of the first page.
For group solutions, include the Gradescope name and email address of every group member. If you are typesetting your solutions with LaTeX, please use our solution template.
- The homework number
- The problem number
- Your Gradescope name
- Your Gradescope email address
- We will not accept late homework for any reason. To offset this rather draconian policy, we will be dropping six homework problems (see the grading policies).
We may forgive coursework under extreme circumstances, such as documented illness or injury. Forgiving homework requires a serious long-term issue that prevents submission of multiple homework sets; the regular homework policies already allow missing a few submissions without serious penalty. “Extreme circumstances” for exams do not include travel for job interviews. We will compute your final course grade as if your forgiven work simply do not exist; your other work will have more weight. Please ask one of the instructors for details.
Form: How to write
Please make it easy for the graders to figure out what you mean in the short time they have to grade your solution. If your solutions are difficult to read or understand, you will lose points.
- Write everything in your own words, and properly cite every outside source you use. We strongly encourage you to use any outside source at your disposal, provided you use your sources properly and give them proper credit. If you get an idea from an outside source, citing that source will not lower your grade. Failing to properly cite an outside source—thereby taking credit for ideas that are not your own—is plagiarism.
The only sources that you are not required to cite are the official course materials (lectures, lecture notes, homework solutions, and exam solutions from this semester) and sources for prerequisite material (which we assume you already know by heart).
- List everyone you worked with on each homework problem. Again, we strongly encourage you to work together, but you must give everyone proper credit. If you work in a group of 20 students, then all 20 names should appear on your homework solution. If someone was particularly helpful, describe their contribution. Be generous; if you're not sure whether someone should be included in your list of collaborators, include them. For discussions in class, in labs, in office hours, or in other large groups, where collecting names is impractical, it's okay to write something like "discussions in class" or "Tuesday evening Grainger study group".
Please see our academic integrity policy for more details.
You will lose points if the graders find your work difficult to read. Writing legibly also helps you think more clearly.
We strongly recommend typesetting your homework, especially if you have sloppy handwriting. We recommend using LaTeX, but you are welcome to use whatever program and/or markup language you like. We will provide a LaTeX template for homework solutions.
You are welcome to submit scans of hand-written homework solutions, provided they are clear and easy to read. We strongly recommend writing with a black ink on white unlined paper, using a scanning app instead of a raw photo, and printing your scanned document to check for readability before submitting. Please do not submit your first draft.
The graders have complete discretion to decide whether a submission is difficult to read. In borderline cases, the graders will first give a warning, asking the student for specific improvements in future homework submissions, rather than immediately deducting points. Please take this feedback seriously.
You will lose points for poor spelling, grammar, punctuation, arithmetic, algebra, logic, and so on. This rule is especially important for students whose first language is not English.
We can only grade what you actually write, not what you mean. We will not attempt to read your mind. If your answer is ambiguous, the graders are explicitly instructed to choose an interpretation that makes it wrong.
- Avoid the Three Deadly Sins. Yes, we are completely serious about these.
- Write solutions, not examples. Don't describe algorithms by showing the first two or three iterations and then writing "and so on". Similarly, don't try to prove something by demonstrating it for a few small examples and then writing “do the same thing for all $n$”. Any solution that includes phrases like “and so on”, “etc.”, “do this for all n”, or “repeat this process” automatically gets a score of zero. Those phrases indicate precisely where you should have used iteration, recursion, or induction but didn’t.
- Declare all your variables. Whenever you use a new variable or non-standard symbol for the first time, you must specify both its type and its meaning, in English. Similarly, when you describe any algorithm, you must first describe in English precisely what the algorithm is supposed to do (not just how it works). Any solution that contains undeclared variables automatically gets a score of zero, unless it is otherwise perfect. This rule is especially important for dynamic programming problems.
- Never use weak induction! Always, always, always use a strong induction hypothesis, even in proofs that only apply the induction hypothesis at n-1. Why would you even want to tie n-2 hands behind your back? Any proof that uses a weak induction hypothesis automatically gets a score of zero, unless it is otherwise perfect. Basically, weak induction should die in a fire.
- Don't submit your first draft.
Revise, revise, revise. First figure out the solution, then think about the right way to present it, and only then start writing what you plan to submit. See also "write legibly".
- State your assumptions.
If a problem statement is ambiguous, explicitly state any additional assumptions that your solution requires. (Please also ask for clarification in class, in office hours, or on Piazza!) For example, if the performance of your algorithm depends on how the input is represented, tell us exactly what representation you require. Yes, even if the assumption is “obvious”.
- Don't submit code.
Describe your algorithms using clean, human-readable pseudocode. Your description should allow a bright student in CS 225 to easily implement your algorithm in their favorite language, using a software library containing implementations of every algorithm we’ve seen in class.
- Keep it short. Every homework problem can be answered completely in at most two typeset pages or five handwritten pages; most problems require considerably less. Yes, I am aware of the crushing irony.
- Omit irrelevant details. Don't write "red-black tree" when you mean "balanced binary tree" or "dictionary". Don't write "depth-first search" when you mean "whatever-first search". Don't submit code; we want to see your ideas, not syntactic sugar. If your solution requires more than two typeset pages, you are providing too many irrelevant details.
Don't regurgitate. Don't explain binary search; just write "binary search". Don't write the pseudocode for Dijkstra's algorithm; just write "Dijkstra's algorithm". If the solution appears on page 6 of Jeff's notes, just write "See page 6 of Jeff's notes." If your answer is similar to something we've seen in class, just say so and (carefully!) describe your changes. You will lose points for vomiting, especially if you get the details wrong.
Don't bullshit. We will give an automatic zero to answers which we consider to be too long, unclear, and repetitious. We will also do it if we can not follow the logic of your answer. We might even do it without reading them.
Content: What to write
- Answer the right question. No matter how clear and polished your solution is, it's worthless if it doesn't answer the question we asked. Make sure you understand the question before you start thinking about how to answer it. If something is unclear, ask for clarification! This is especially important on exams.
By default, if a homework or exam problem asks you to describe an algorithm, you need to do several things to get full credit:
Some problems may deviate from these default requirements. For example, we may ask you for an algorithm that uses a particular approach, even though another approach may be more efficient. (Answer the right question!)
- Describe the problem that your algorithm is supposed to solve. This is often the hardest part of designing an algorithm. See the second Deadly Sin.
- Give a concise pseudocode description of your algorithm. Don't regurgitate, and don't turn in code!
- Describe a correct algorithm.
- Justify the correctness of your algorithm. You must provide a brief justification for your solutions, as evidence that you understand why they are correct. Unless we explicitly say otherwise, we generally do not want a complete proof of correctness—because complete proofs would be too long, tedious, and unenlightening—but rather a high-level sketch of the major steps in the proof. Correctness arguments are required on exams only when we specifically ask for them.
- Analyze your algorithm's running time. This may be as simple as saying "There are two nested loops from 1 to n, so the running time is O(n²)." Or it may require setting up and solving a recurrence, in which case you'll also have to justify your solution.
- Describe the fastest correct algorithm you can, even if the problem does not include the words "fast" or "efficient". Faster algorithms are worth more points; brute force is usually not worth much. We will not always tell you what time bound to shoot for; that's part of what you're trying to learn. However, if your algorithm is incorrect, you won't get any points, no matter how fast it is!
“I don't know”
- In some previous semesters, we used to give IDK (I dont know) points. We will not do this semester as it seems to discriminate against people that know what they are doing, but are not sure about it.
IDK points make sense when one enforces aggressive policies of giving zero for solutions that are not very close to being correct. Naturally, students hate such aggressive grading policies.