This is the mother of dynamic programming algorithms in my opinion. It computes
the minimal "edit distance" between two input strings where an edit is
considered one of:
- inserting a character into `a`
- deleting a character from `a`
- substituting a character in `a` with a character from `b`
It took me awhile to grok the algorithm, but I implemented this from my
understanding of something that I read ~3 nights prior, so I must've understood
what I read. Good news!
This morning, I attended the "Interview Club" and was asked this question by the
interviewer in front of ~20 FTEs. While I struggled to fully solve it during the
abridged (i.e. 20 minute) timeslot, I completed the problem afterwards.
Here is my solution.
Create a suffix tree from an input string. This implementation uses a stack to
control the flow of the program.
I expected this attempt to be easier than my first attempt, but surprisingly, it
was similarly difficult. It took me ~30-45 minutes to successfully implement
this function, and I'm still not pleased with the final result.
While it took me awhile to implement, this exercise was definitely worth
doing. I think there should be a more elegant way to construct the tree using
maybe a stack, but I couldn't find it.
All of this was part of a larger effort to search a string for a variety of
patterns. The solution is to compile the string into a suffix tree and then
search the suffix tree for each of the patterns.
I'm glad I didn't gloss over this exercise.
Passing a string directly to add_paths like this causes the proto class
to take ownership over the string, meaning when it is destructed it
will *explicitly* free the string. When the string's actual owner (the
derivation struct) then goes out of scope it'll get freed again, causing
a double-free. This fixes that to instead use the copy constructor to
assign to a pointer to a new path, and covers the whole to_proto method
with a rapidcheck test.
Fixes: b/64
Change-Id: I84235bed9104ff430a0acf686d4a96f1e2e9a897
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2106
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI
This was accidentally using the proto arena API to assign the derivation
field of a BuildDerivationRequest. We *thought* this was causing a
double free, but even with this change that's still happening. That
said, this change is probably still a good idea since it's using the
proto API as intended.
References: b/64
Change-Id: I950a4eafb214e9113639ea54d2dfd4659b7be931
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2104
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
This reverts commit 2e2bdf9c6c.
Reason for revert: this is not working, and is resulting in newly created issues just showing a blank page (b/74)
Change-Id: I3f06afc52d6c5289269402fc75bb32ad9c376bf4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2082
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
- htop has moved upstreams, which has been producing new releases, so
update the derivation to pull from the new repository on GitHub.
- All of the patches I have locally have been merged upstream, so drop
them from the depot.
- Pull from a reasonably recent git commit instead of from a numbered
release, as the ZFS ARC stats and CPU meter columnation patches
haven't made it into a release yet.
Change-Id: I66ad4c035df07709abf4f75a9d4e1486920091d0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2105
Reviewed-by: multi <depot@in-addr.xyz>
Tested-by: BuildkiteCI
This file represents the static pipeline which is configured in the
Buildkite web UI. Updates to this file should be applied in the admin
interface.
These steps are responsible for launching the dynamic pipeline
evaluation, or falling back to the fallback pipeline if evaluation fails.
Change-Id: I6d7dd623cde65e8c69faea729f737c9bba00c2fb
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2103
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
This adds a simple fallback Buildkite pipeline configuration which
always fails the pipeline, but correctly reports back the failure
status.
Note that this also requires changes in the Buildkite configuration
that is not in version-control.
Relates to b/66.
Change-Id: I6802a6f76448c3893798a06d514e6ccba0f50dd2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2102
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
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.
Adds configuration options for the (inconsistently named) environment
variables that configure irccat integration with Panettone.
The defaults match the irccat setup on whitby.
Change-Id: I6857512a2e3f29f16777493eb981cc69ce3c045f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2080
Tested-by: BuildkiteCI
Reviewed-by: kanepyork <rikingcoding@gmail.com>
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.
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.
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.
for some reason installing it directly via nix doesn't work atm, so I
have this hack here
Change-Id: I45093633c35e756988078eb136c6e7bc3c532eea
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2078
Reviewed-by: glittershark <grfn@gws.fyi>
Tested-by: BuildkiteCI
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.
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.
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.
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.
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.
- The new PANETTONE.IRC package contains the SEND-IRC-NOTIFICATION function,
which opens a new TCP socket to irccat (if it's running and configured) in
order to announce the creation of new issues.
- The IRCCATHOST and IRCCATPORT environment variables must be set for this to
work.
- Additionally, the ISSUECHANNEL environment variable may be used to direct
announcements at a given channel (otherwise it'll just use the first one).
Change-Id: I429a66f24d0f80ed10db173d6af7105fb1d3d023
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2077
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
This module configures irccat by creating a JSON configuration file
from a user-supplied Nix struct (this is not checked for correctness),
and merging it recursively with secrets from
`/etc/secrets/irccat.json` at service launch time.
This way we get the ability to configure (most) options declaratively
via Nix, while providing the secrets outside of Nix.
Side note: We need to figure out a secrets distribution mechanism.
Tested: Wrote a dummy config in whitby/default.nix locally and checked
that this builds, but I have not actually run the service yet. I
expect that some minor tweaks will end up being necessary.
Change-Id: I02a2e8dc40a7f8417fd77afcf8a12ac3df117988
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2074
Tested-by: BuildkiteCI
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: glittershark <grfn@gws.fyi>
This is to be used for forwarding messages to our IRC channels.
Change-Id: I6362c6f50a22f504588a7161d41a170f4e7a6edc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2073
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
Reviewed-by: lukegb <lukegb@tvl.fyi>
Machines on which LANG is misconfigured have trouble with SBCL loading
files that contain characters in certain encodings. This overrides
whichever local LANG (if any) is set.
Change-Id: Ic4341a01c4393e7f697de6cecc58dea4f2d85987
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2076
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
... this should also update my system EXWM.
Change-Id: Idfbbda67613ac678dc2d5f82533e1c6176ab4a28
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2072
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
... I found this location in the logs, because the certs are now valid
for this, but I'm not actually sure if it's right.
Change-Id: I5ac88073e3bf6a95fead4c1d34515622c4416c6a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2070
Tested-by: BuildkiteCI
Reviewed-by: lukegb <lukegb@tvl.fyi>
Sometimes (like today) paroxysm crashes. We'd like it to restart if that
happens.
Change-Id: I98841096bcd6605c4279744ae5c65a9c92092a21
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2069
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
