Commit graph

112 commits

Author SHA1 Message Date
William Carroll
c0268ed31a Refactor random-choice
Prefer initializing `result` to an empty array of size `m`, which makes the
algorithm a bit more elegant.
2020-11-17 23:54:54 +00:00
William Carroll
751b5327a9 Solve algorithms dealing with randomness
Tonight I learned that random sample where each element in the sampling corpus
has an equal likelihood of being chosen is a brand of algorithms known as
"reservoir sampling".

- Implement random.shuffle(..)
- Implement random.choice(..)

Surprisingly, candidates are expected to encounter problems like this during
interviews.
2020-11-17 22:28:24 +00:00
William Carroll
572fb0fe5f Solve "nearby words" function
Given an input like "gello" suggest an correction like "hello".

This is a proof-of-concept problem for writing a simplistic auto-correction
algorithm for a mobile device.
2020-11-16 17:17:28 +00:00
William Carroll
6989c3a91a Implement the Rabin Karp string matching algorithm
This algorithm is pretty interesting because it runs in linear time with respect
to the length of the `corpus` string. It does this by using a sliding window
hash. This hash -- because it's a sliding window -- runs in constant time for
each iteration; we're only adding and subtracting one character each time and
not re-hashing the whole "window".

When our hashes match, only then do we compare the "window" to the
`pattern`. String comparisons are linear because they compare each character to
each character one at a time. But because we only compare strings when are
hashes match (a check which runs in constant time), this spares us the
performance hit.
2020-11-16 17:14:08 +00:00
William Carroll
a2fa88f561 Prefer mutative variant of delete for HashTable
Instead of calling `filter(..)`.
2020-11-16 17:13:39 +00:00
William Carroll
a457a81bbb Add another solution to the "move zeroes to end" problem
Support the optimally performance solution of which I'm aware.
2020-11-16 17:13:03 +00:00
William Carroll
ff08b723db Solve "find pairs for sum"
I have encountered this problem 3x in the wild thus far:
  1. www.InterviewCake.com
  2. Cracking the Coding Interview
  3. www.Pramp.com
2020-11-16 17:12:05 +00:00
William Carroll
92ab94943e Start working on the "Hard" problems
Firstly, implement a function that adds two arguments together... without using
the `+` operator. I need to drill this problem. Thankfully I took a Coursera
course that taught me how to make a half-adder and a full-adder, but the
recommended solution for this is a bit more difficult.
2020-11-16 17:10:57 +00:00
William Carroll
30f4d6f4a4 Implement a simple hash function and hash table
I was always curious how hashing functions were implemented, so I read about the
"polynomial rolling hash function", and I decided implementing it would be a
good exercise. After writing that, writing a hash table was simple.
2020-11-16 00:35:01 +00:00
William Carroll
363519273a Find the intersection (if any) between two linked lists
As with most linked list questions, this one involves an arcane trick from the
neck-bearded playbook.
2020-11-15 17:42:44 +00:00
William Carroll
c8330adfcb Solve "Move Zeroes to End"
Write a function to modify an array of integers in-place such that all of the
zeroes in the array are at the end, and the order of the other integers is not
changed.
2020-11-15 13:51:46 +00:00
William Carroll
09cd819a70 Include re-roll strategy for rand7
After seeing the solution that my book advocated, I implemented it using
recursion.
2020-11-14 17:36:04 +00:00
William Carroll
5820f6f459 Solve rand7
Write a random number generator for [0,7) using only a random number generator
for [0,5). Ensure the results are uniformly distributed.
2020-11-14 17:26:00 +00:00
William Carroll
a0e9e2b310 Solve unsorted-substring a second time
This solution operates in O(n) time instead of O(n*log(n)) time, which
surprisingly isn't *that* big of a difference...

Consider a size of n of 10M...
  1) ~10s
  2) ~0.5s

So, yes, the O(n*log(n)) will take 100x longer to complete, but for an enormous
input size of 10M elements, it can still complete in under a minute. The
difference between that and the second, faster, algorithm, is just 9s.
2020-11-14 15:28:23 +00:00
William Carroll
48fde5f278 Solve unsorted-substring
Write a function that returns the indices demarcating a substring, which if
sorted, would make the entire array sorted.
2020-11-14 15:08:25 +00:00
William Carroll
47c5c6ac05 Partially implement a Heap
Defining the insert (or "siftup") function described in the "Programming Pearls"
book.
2020-11-14 14:08:58 +00:00
William Carroll
c841527f61 Write encoded XML parser and pretty-printer
Write a function that reads a string of compressed XML and outputs the
decompressed version.

Note to self: Now that I'm growing more comfortable writing parsers, I'd like to
become equally comfortable writing pretty-printers.
2020-11-14 14:00:00 +00:00
William Carroll
bfd2180e6b Solve tic-tac-toe checker
Write a function that verifies whether or not a tic-tac-toe board is valid.
2020-11-13 17:45:07 +00:00
William Carroll
1b3f1b99f5 Solve box-stacking problem
Write a function to compute the highest stack of boxes that can be created from
a list of boxes.
2020-11-13 16:57:47 +00:00
William Carroll
7672049e1c Solve N queens
After a five year hiatus, I decided to attempt to solve the famous N queens
problem again. This time, instead of modeling the chess board using a
`[[Bool]]`, I'm using `[Integer]` where the `Integer` indicates which column has
a queen. This is a bit lighter in RAM.
2020-11-13 16:56:02 +00:00
William Carroll
14f6169fcf Document subset of BNF for regex engine
Adding some documentation for my future self.
2020-11-13 16:55:39 +00:00
William Carroll
aa66d9b83d Add coding exercises for Facebook interviews
Add attempts at solving coding problems to Briefcase.
2020-11-12 14:37:29 +00:00
William Carroll
69b6bda01b Style habit screen to accommodate footer
Add spacing to the bottom to make space for the footer.
2020-11-12 11:19:30 +00:00
William Carroll
2290aac2a8 Tweak styles
Add spacing to help the app breathe.
2020-10-11 16:47:31 +01:00
William Carroll
767fed75c3 Support multiple HabitTypes
I could have and should have broken this change into smaller pieces, but when I
came up for air, I had changed too much, and most of the changes are
intermingled. Oh well... this is an exciting change!

Include habits for:
- Morning
- Evening
- Payday (the 25th)
- First of the Month
- First of the Year

Since the Morning and Evening routines might be a bit noisy, I'm excluding them
from the output using a flag, `include{Morning,Evening}`, which I support in the
UI to toggle their visibility.

I made *much* more progress on this app that I expected to today, and I *think*
-- short of supporting a database and a server -- I'm close to
being *completely* finished.

Wahoo!
2020-10-11 16:40:10 +01:00
William Carroll
abf1875934 Support Msg to clear all completed tasks
Add a simple button to clear all completed tasks.
2020-10-11 15:39:01 +01:00
William Carroll
79cf42abd5 Render time remaining in UI
Show the number of minutes remaining before completing all of the tasks.
2020-10-11 15:17:20 +01:00
William Carroll
5684608fed Move tailwind function into Utils module
Instead of accepting `List (String, Int)`, accept `List Strategy` where
`Strategy` defines whether or not the string of selectors should be applied to
the element.

I'm also renaming it `class` so I can just use `Utils.class`; `tailwind` has
little to do with the function itself.
2020-10-11 14:59:42 +01:00
William Carroll
1c8a8f5d2c Expand Habit type
Include:

- habitType: Daily, Weekly, Yearly... what's the trigger?
- minutesDuration: Estimation of how long it'll take to complete
2020-10-11 14:58:49 +01:00
William Carroll
05d52e403c Tweak styles
- Change header to blue
- Change habit to gray when completed
- Prefer app font for footer instead of monospaced font
2020-10-11 10:24:11 +01:00
William Carroll
0a15ea7366 Create UI module for common components
Create UI.elm to house components like `button`, which is a simple HTML button
with `focus:outline-none` applied as a `class`, which is an accessibility
feature that I don't need for this touch-screen application.

I like this pattern more than my more opinionated patterns for UI modules in Elm
where I'd define all of the arguments as a record type (i.e. kwargs).
2020-10-11 10:15:03 +01:00
William Carroll
106457de4b Prefer handwritten font
Use the Google Fonts API to fetch a handwritten font, which gives the app a
modicum of personality. There are more "best practices" ways to do this, such
as:

- Download the font once, and include it in the bundle
- Extend the Tailwind configure to recognize the font
- Ditch the inline <style> block

But I don't need the performance benefits that the first bullet provides. And
the second two bullets are more relevant for a larger application with more than
one font. So I think in this case, the easiest solution is best.

Also:
- Use `container` and `mx-auto` to constrain content for wide screens
2020-10-11 10:09:15 +01:00
William Carroll
19fbdad1c0 Support viewing different days
Allow users to browse the habits of the other days of the week.
2020-10-10 18:20:24 +01:00
William Carroll
487232d1aa Ensure weekday is updated
This ensures us that our view is consistent within ~1 minute of reality.
2020-10-10 17:34:14 +01:00
William Carroll
7d425de48d Tweak styles
- Increase font size for header
- Prefer a bulleted list
- Reduce horizontal padding
2020-10-10 17:31:34 +01:00
William Carroll
bfbe7dc988 Add a footer
With personal information and information about the project's stack.
2020-10-10 17:31:00 +01:00
William Carroll
df8e45681d Remove Nap from Saturday; prefer Yin Yoga
Since Warm Yin Yoga is at 15:00, it's difficult to attend that *and* nap.
2020-10-10 17:30:22 +01:00
William Carroll
9d331f3077 Begin working on Habit Screens project
Created a small MVP for digitizing my weekly habits. Much more to come.

Lots of things happening:

- Copied the boilerplate to get started
- Added a brief project-level README
- Outlined my ambitions in design.md

See README and design.md for more context on this project.
2020-10-10 17:04:24 +01:00
William Carroll
0f160a8029 Ignore comments in output for grocery export
TL;DR:
- Ignore lines starting with "#"
- Tidy up the code
2020-10-03 11:00:11 +01:00
William Carroll
a7aef84408 Update my grocery list for Bermondsey London
I haven't updated this list since I was living in Dargow, Germany over the
summer. Now that I've settled down, and I'm situated in the London Bridge area,
I'm updating the list.
2020-10-03 11:00:05 +01:00
William Carroll
33890d8a8b Move scratch/brilliant into //assessments
Where it belongs...
2020-08-20 11:26:32 +01:00
William Carroll
0c71fc9d1d Drop support for dir-locals.nix, <nixpkgs>, etc.
In the spirit of Marie Kondo, I'm tidying up!

TL;DR:
- Prefer .envrc `use_nix` and delete all dir-locals.nix files
- Remove ~all references to <nixpkgs>, <unstable>, <depot> and prefer
  referencing each with briefcase.third_party.{pkgs,unstable,depot}
- Delete nixBufferFromShell function since I was only using that in
  dir-locals.nix files
2020-08-20 11:26:32 +01:00
William Carroll
59f7481411 Revise previous opinions about absolute paths GT <bracket-notation>
Unforeseen problem: `buildkite-agent` runs its builds in a separate directory,
so if I want the `nix-build` command to build the newly checked out code, I need
to set <briefcase> to the CWD.
2020-08-20 11:26:31 +01:00
William Carroll
2da4b12266 Consume buildHaskell functions
Use the newly defined `buildHaskell` function for a few of my existing Haskell
projects. So far, it works as intended!
2020-08-12 16:28:39 +01:00
William Carroll
bba3f16c43 Prefer snake-shift instead of a row-by-row shift
Per the assignment's instructions, the `Shift n` operation should treat
the *entire keyboard* like a cycle and shift that. I was erroneously
treating *each row* like a cycle and shifting those one-by-one.

This change fixes that. In addition, it also:
- Updates README.md with expected inputs and outputs
- Updates test suite
- Adds `split` dependency to {default,shell}.nix
2020-08-12 12:03:35 +01:00
William Carroll
f11b91c985 Adds property tests to generically test keyboard transformations
Tests:
- HorizontalFlip
- VerticalFlip
- Shift n
2020-08-12 11:27:06 +01:00
William Carroll
f3ddd89302 Prefer literal, not computed, examples in the unit tests
TL:DR:
- Remove unused imports: Test.QuickCheck and Control.Exception
- Remove calls to `reverse` and `Utils.rotate` with their results
2020-08-12 11:07:37 +01:00
William Carroll
3d6130c7cf Provide more useful instructions for building this project
TL;DR:
- include a default.nix to allow users to build an named executable
- emphasize in the README that the user needs Nix to build this project
- pin nixpkgs to a specific commit and fetch it from GitHub
2020-08-12 10:28:04 +01:00
William Carroll
17e1764ef8 Generate coords function from existing qwerty keyboard
Per my take-home assignment's reviewer's comments, with which for the record I
agree, I should generate the character->coordinate table from my existing qwerty
keyboard definition.

The best part is: by doing this I found a bug: Notice how the original '0'
character was mapped to the Coordinate (0,0)... thus every subsequent digit
key (i.e. the first row) is off-by-one.
2020-08-12 09:46:36 +01:00
William Carroll
5f52077492 Re-type type using the altered keyboard
Remember: always read the instructions; that's the most important part.
2020-08-06 00:18:44 +01:00