**Here are the problem archives from fall 2021. Solutions may be found in the following URL: https://github.com/PrincetonACM/Archive-COSCON-Fall-2021**

## Some Helpful Tips

**Every problem statement has a description of how to submit a solution. **Ask us if anything isn’t clear! In general, each problem will either require you to make a submission on the corresponding page of our HackerRank contest or by email to coscon.written.submission@gmail.com with a subject line of *ProblemXSubmission* (here, *X* is the problem number that you’re submitting a solution too). - Problem 7 is an exception to the email rule, where an autograder has been set up for you. In this case, you are to email your submissions to coscon.interactive.grader@gmail.com. See the problem statement for more details!
- We recommend that you start with problem zero — though if you’re gunning for the prize for the fastest solution, you might choose to ignore this advice (the fastest solution to problem zero doesn’t count).
- Problems have varying point values.
- So of the problems will require you to submit a write-up or a proof. You may write your answers by hand or type them, but be warned that we will make little to no effort reading illegible solutions.
- All your submissions (both on HackerRank and in your Drive) must be in by
**7:30 PM EST**. Submissions after then will be ignored. - Don’t hesitate to reach out either by email or by stopping by at office hours (in McDonnell)! We would love to meet you all.

## Problem 0: Climbing the Corporate Ladder [HackerRank]

##### This problem is a warm-up to get you excited and familiar with the HackerRank interface. This problem is worth **5 points**. Download the problem statement below:

## Problem 1: Bamboozling Big Oil [HackerRank]

##### This problem is worth **15 points**. Download the problem statement below:

## Problem 2: Lord of the Lanternflies [Email Submission]

##### This problem is worth **15 points**. Download the problem statement below:

## Problem 3: Solace of Quantum [HackerRank]

##### This problem is worth **15 points**. Download the problem statement below:

## Problem 4: Yeast Colonies [Email Submission]

##### This problem is worth **15 points**. Download the problem statement below:

##### All the directions that you need to follow are in the problem statement and the Colab files it will lead you to. If anything is unclear, or if Colab isn’t working, or if you are confused as to how to start, come to office hours or ask on the Discord!

## Problem 5: Stackland [Email Submission]

##### This problem is worth **15 points**. Download the problem statement and the auxiliary files you’ll need below:

## Problem 6: The Tiger Casino [Email Submission]

##### This problem is worth **25 points**. This problem is quite hard, so we’ll be giving generous partial credit. Download the problem statement and the auxiliary files you’ll need below:

##### All the directions that you need to follow are in the problem statement. But if your goal and/or the layout of the code you’ve been given is unclear, come to office hours or ask in the Discord!

**A note on grading**: Anyone who has a positive win rate on the test randomness will get full credit for the writeup (although be aware that because the testing randomness is different than the sample randomness; your win rate may differ by a percent or two from what you see locally). Among those who do have positive win percentage, we will grade by clustering but will very likely not be giving full credit to any solution that doesn’t do very well (a narrow 5-6% edge wouldn’t suffice).

## Problem 7: Welcome to Recursion Hell [Email Submission]

##### This problem is worth **15 points**, with the possibility of **15 points** of extra credit. This problem is quite hard, so we’ll be giving generous partial credit. Download the problem statement below:

##### All the directions that you need to follow are in the problem statement. But if your goal and/or parts of the problem statement are unclear, come to office hours or ask in the Discord! *Also remember that even though this is an email submission, the submission email and directions are slightly different. Refer to the problem statement.*

## Problem 8: Optimal Search Trees [HackerRank, Email for Extra Credit]

##### This problem has two parts; solving either of them nets you **15 points**. *You don’t need to do both parts.* Also, there is an opportunity to get **3 points of extra credit**. Download the problem statement below: