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2020-12-25 Finish Tree section of LC problemsWilliam Carroll1-3/+3
Wahoo! I need to remember that the inorder traversal of a BST should be sorted. This piece of trivia comes in handy for a variety of BST related problems. I also think being able to do a {pre,in,post}-order traversal recursively and iteratively is a skill that I need to develop.
2020-12-25 Solve a few String questionsWilliam Carroll1-3/+3
Valid Anagram This one is a classic: `sorted(a) == sorted(b)` Group Anagrams Using product of prime numbers to create a key for anagrams is much faster than sorting the characters in each word. It is also satisfyingly simple. Encode and Decode Strings My initial implementation was clumsy and prone to fail for edge-cases. A more elegant solution is using something like: ```python def encode(words): return "".join("{}:{}".format(len(x), x) for x in words) ```
2020-12-25 Tread lightly into the Dynamic Programming sectionWilliam Carroll1-1/+1
After solving this, I was immediately stumped by the other DP questions, so I'm taking a break.
2020-12-25 Solve Binary "Sum of Two Integers"William Carroll1-1/+1
This is tricky because Python has variable-width integers, so relying on two's complement to support the sum of negative numbers results in infinite recursion. I know three ways to combat this: 1. Use Java. 2. Conditionally branch and handle either addition or subtraction accordingly. 3. Use a mask to enforce fixed-width integers in Python.
2020-12-22 Solve additional Tree problemsWilliam Carroll1-4/+4
Only three more to go!
2020-12-22 Solve additional Matrix problemsWilliam Carroll1-3/+3
Looks like "Rotate Image" is the only Matrix problem that remains. It was nice to learn more about "Backtracking" -- a term I often encounter -- while attempting to solve "Word Search". From my current understanding, it is like Brute Force but with short-circuiting. It also seems quite similar to Depth First Search, and I'm currently unaware of how DFS and Backtracking differ. I'm hoping to learn more though.
2020-12-18 Solve the Linked List questionsWilliam Carroll1-2/+2
I did these during my flight from LON->NYC without wifi. I managed to get both correct on the first attempt although I did not find the *optimal* solution for "Reorder List". IMO "Reorder List" is the best Linked List question I've seen because it covers a few essential Linked List tricks.
2020-12-18 Nest URLs beneath TODO entriesWilliam Carroll1-76/+151
Tidying things up.
2020-12-18 Update remaining LC questionsWilliam Carroll1-9/+9
Looks like I should prioritize the following topics: - Dynamic Programming - String - Graph Although I'm not sure how common DP questions are in interviews, DP is a useful dragon to slay IMO.
2020-12-18 Update Linked List LC questionsWilliam Carroll1-4/+4
Snapshot my progress with Linked Lists...
2020-12-18 Update LC String questionsWilliam Carroll1-2/+2
Looks like I have a few string questions to solve before closing that chapter.
2020-12-18 Mark LC Tree questions as doneWilliam Carroll1-7/+7
Making sure that this document closely approximates the state of my LC progress.
2020-12-18 Create offline, org file from TeamBlind LC questionsWilliam Carroll1-0/+88
TeamBlind.com hosts a curated list of DS&As questions from LeetCode.com that the author claims appropriately samples the topics worth exploring. I'm creating an offline list so that I can track my progress and work while I'm traveling.
2020-12-13 Show Morning and Evening habits by defaultWilliam Carroll1-2/+2
Now that I've deployed this, and I have an iPad running in kiosk mode, I realized that I'd like to show my morning routine and my evening routine.
2020-12-13 Update Sunday and Morning chainsWilliam Carroll1-3/+1
Adapting to changes.
2020-12-13 Add -r to cp to copy the directoryWilliam Carroll1-1/+1
This should be the last hold-out before deploying habit-screens! :)
2020-12-13 Commit compiled file, output.css to habit-screensWilliam Carroll2-1/+103571
As you can see, I was previously `.gitignore`-ing this file, but because my `default.nix` attempts to `cp output.css`, I need that file available.
2020-12-13 Productionize habit-screensWilliam Carroll2-12/+20
At some point I should document or write a script for how I package Elm projects with Nix to be deployed on my website. For now, I'm modeling everything after my previous success LearnPianoChords.
2020-12-12 Add project-local .gitignoreWilliam Carroll1-0/+1
Since the `default.nix` file is specific to my tooling, I'm ignoring it.
2020-12-12 Add usage instructions to top-level READMEWilliam Carroll2-21/+14
Also delete redundant `README` from `server` directory.
2020-12-12 Expose functions at API layerWilliam Carroll4-2/+104
Creating a simple HTTP RESTful API for exposing our `Server.semiprime` function. It supports some help messages, primitive parsing and error handling, and singular vs. batch processing of arguments. For more sophisticated parsing and error-checking, I prefer to use Haskell's Servant library.
2020-12-12 Include cache hit/miss info in return typeWilliam Carroll2-3/+4
This can be useful downstream for diagnostics.
2020-12-12 Expand 10^5 in READMEWilliam Carroll1-1/+1
I think it's more readable this way.
2020-12-12 Simple Math testsWilliam Carroll1-3/+1
Calling `assert` within the `Enum.map` makes the errors more usable.
2020-12-12 Define Server.semiprimeWilliam Carroll2-9/+49
- Clear the boilerplate that `mix` generated - Consume `Math.factor` to test which inputs are semiprimes - Cache all inputs that are semiprimes as soon as we discover that they are - semiprimes I considered a couple things related to the Cache: - Could save space by storing all semiprime factors in a tree. This would make the lookups more expensive. Also because the tree's depth would never exceed two (because all semiprimes only have two factors), the tree would be quite broad, and we may not be saving enough space for the trade to be worthwhile. I might be wrong about that though. - We could consider pre-computing all semiprimes when we start the app, but without running some tests firsts, I'm not sure whether or not it's worth the trouble.
2020-12-12 Define Cache.{list,clear} to help debuggingWilliam Carroll1-0/+14
Since I'm often using `iex` for interactive development, these functions are useful.
2020-12-12 Define Cache and convert app to OTPWilliam Carroll4-1/+58
Define a simple in-memory key-value store for our cache. TL;DR: - Define `Cache` as a simple state-keeping `Agent` - Define `Sup`, which starts our Cache process - Define `App`, which starts our Supervisor process - Whitelist `App` in `mix.exs`, so that it starts after calling `iex -S mix`
2020-12-11 Add moduledoc to ExtrasWilliam Carroll1-0/+4
9 out of 10 doctors agree that every module needs a doc. Ask your doctor if moduledocs are right for you!
2020-12-11 Move the habit-screens project into //websiteWilliam Carroll17-18/+149
I'd like to eventually deploy this to wpcarro.dev. Coming soon!
2020-12-11 Delete //website/habitsWilliam Carroll2-17/+0
Accommodating space for my habit-screens project.
2020-12-11 Delete //website/habitgardenWilliam Carroll15-5904/+0
This is change #2 in a series of other larger changes...
2020-12-11 Delete //website/days-of-week-habitsWilliam Carroll15-6048/+0
This is one small change in a series of other, larger changes.
2020-12-11 Define stubbed default.nixWilliam Carroll1-0/+1
In case I want to package this project with Nix. For now, it's useful to store this at the project root because it help my Emacs's `project-find-file` function.
2020-12-11 Define Math moduleWilliam Carroll2-0/+58
Support `Math.factor` and cover it with tests.
2020-12-11 Define Extras moduleWilliam Carroll2-0/+36
I'll use as the host for utility functions needed to extend the stdlib.
2020-12-11 Init Elixir projectWilliam Carroll8-0/+107
Starting fresh with... ```shell mix new server ```
2020-12-11 Initialize the Semiprimes ServiceWilliam Carroll1-0/+30
This is an exciting take-home assignment because I get to write a service in Elixir!
2020-12-07 Update groceries/list.orgWilliam Carroll1-39/+76
Oh the times they are a-changin'
2020-12-07 Define another function to illustrate Reservoir SamplingWilliam Carroll1-0/+11
Documenting a few ideas about Reservoir Sampling while it's fresh on my mind.
2020-12-07 Fix typoWilliam Carroll1-1/+1
It's Splitwise... not Transferwise!
2020-11-23 Update BFS implsWilliam Carroll2-3/+3
I've subtly been implementing breadth-first traversals in graphs incorrectly. The change is subtle, but updating `seen` needs to happen immediately after queuing an item. The results will remain the same, but the runtimes will differ dramatically. I didn't notice this until I attempted to complete LeetCode's "count islands" challenge, and LeetCode rejected my solution because it could not finish before timing out. After looking at other candidates' solutions and comparing them to mine, I couldn't see any difference... except for this subtle difference. This SO answer provides a helpful explanation: https://stackoverflow.com/questions/45623722/marking-node-as-visited-on-bfs-when-dequeuing The take-away lesson here is to always call `seen.add(..)` immediately after enqueuing.
2020-11-21 Solve "cafe order checker" (again)William Carroll1-0/+34
Perhaps my fifth iteration of solving this problem.
2020-11-21 Solve "permutation palindrome" (again)William Carroll1-0/+8
Python's `collections` library really shines for this problem.
2020-11-21 Implement a queue using two stacksWilliam Carroll1-0/+17
The space cost is O(n). The runtime cost of enqueue is O(1); the runtime cost of dequeue is O(n). Using the "accounting method", the cost of an item in the system is O(1). Here's why: +------------+----------------------------+------+ | enqueue | push onto lhs | O(1) | +------------+----------------------------+------+ | lhs -> rhs | pop off lhs; push onto rhs | O(1) | +------------+----------------------------+------+ | dequeue | pop off rhs | O(1) | +------------+----------------------------+------+
2020-11-21 Implement a bottom-up fibonacciWilliam Carroll1-0/+6
The bottom-up solution run in O(n) time instead of O(2^n) time, which the recursive solution runs as: ``` def fib(n): return fib(n - 2) + fib(n - 1) ``` Remember that exponential algorithms are usually recursive algorithms with multiple sibling calls to itself.
2020-11-21 Solve "linked-list-cycles"William Carroll1-0/+70
Write a predicate for checking if a linked-list contains a cycle. For additional practice, I also implemented a function that accepts a linked-list containing a cycle and returns the first element of that cycle.
2020-11-21 Reimplement bst-checkerWilliam Carroll1-0/+14
Practice makes perfect. See the previous commit for a more details about this solution.
2020-11-21 Refactor existing bst-checker implementationWilliam Carroll1-40/+10
I believe the previous solution is invalid. This solution works and it should be more time and space efficient. Space-wise our stack grows proportionate to the depth of our tree, which for a "balanced" BST should be log(n). Doing a BFT on a BST results in memory usage of n because when we encounter the leaf nodes at the final level in the tree, they will be 1/2 * n for a balanced BST.
2020-11-21 Solve merge-sorted-arrays (again)William Carroll1-0/+30
InterviewCake.com has a section on Facebook's interview, so I'm attempting to solve all of the problems on there even if that means I'm resolving problems. The more practice, the better. Right? URL: interviewcake.com/facebook-interview-questions
2020-11-21 Solve "find duplicate" using a graphWilliam Carroll1-0/+57
This problem is unusually difficult, but the solution is elegant.
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