Thursday, 2020-12-03

7,000 dead in Sweden

Tuesday, 2020-12-01

Advent of Code 2020

This blog post is a work in progress

Project website: Advent of Code 2020.

Previous years: 2015, 2016, 2017, 2018. 2019.

I use Perl for all the solutions.

Most assume the input data is in a file called input.txt in the same directory as the file.

A note on scoring

I score my problems to mark where I’ve finished a solution myself or given up and looked for hints. A score of 2 means I solved both the daily problems myself, a score of 1 means I looked up a hint for one of the problems, and a zero score means I didn’t solve any of the problems myself.

My goals for this year (in descending order of priority):

  • get 40 stars or more (75%)
  • solve all problems up until day 15 without any external input
  • solve all problems within 24 hours of release

Link to Github repo.

Day 1 - Day 2 - Day 3 - Day 4 - Day 5

Day 1 - Report Repair

Day 1 - complete solution

Not much to say about this. I used a hash to keep track of the “rest” of the values when comparing.

Apparently this (or at least part 2) is the 3SUM problem which is considered “hard”. I accidentally implemented the standard solution in part 1 so props for that I guess.

I still believe firing up the Perl interpreter and loading the actual file takes longer than just solving part 2 with two nested loops.

Score: 2

Day 2 - Password Philosophy

Day 2 - complete solution

Despite actually being awake and caffienated when the puzzle dropped, I still managed to mess this up. Extra annoying when it’s basically tailor-made for Perl.

Here’s a partial list

  • messed up the initial regex
  • assigned $min and $max to the same value
  • messed up the comparison range in part 1
  • off-by-one error in the indexing in part 2
  • in part 2, tried to use the sum() function from List::Utils but forgot to use parentheses around the array

Score: 2

Day 3 - Toboggan Trajectory

Day 3 - complete solution Day 3 - alternative solution

Veterans of previous AoC’s will get pathfinding flashbacks from this problem’s description, but it turns out it’s a bit simpler - as can be expected for day 3.

I decided before coding to not store the map explicitely as individual coordinates, instead just storing the rows as a text string and unpacking via split when needed.

Another decision was to work with the test input first to confirm my algorithm. That way it would be easier to, for example, print out the rows in case I needed to visually debug.

Score: 2

Day 4 - Passport Processing

Day 4 - complete solution

This is a “M4P” problem - Made for Perl.

Nothing really to say about this. Set the $/ variable to an empty string to import the records as paragraphs.

I used a dispatch table to avoid a giant if/then/else statement.

Day 5 - Binary Boarding

Day 5 - complete solution

I have a massive binary blind spot, so I just knew there was going to be a CS-appropriate simple solution to this. But I just followed the instructions and got the right answer in the end anyway.

Score: 2

Monday, 2020-11-30


Årsta i November II

[Nov 2019] | Nov 2018 | Nov 2017 | Nov 2016 | Nov 2015 | Nov 2014 | Nov 2013 | Nov 2012 | Nov 2011

Thursday, 2020-11-05

6,000 dead in Sweden

Saturday, 2020-10-31

Friday, 2020-10-16

Return of a King: The Battle for Afghanistan by William Dalrymple

A good overview of the First Anglo-Afghan War. The parallels to today’s situation are presented but not in a polemical way. Dalrymple presents “both sides”, avoiding the all too common trope of only focusing on the British defeat and hardships.

Wednesday, 2020-09-30

Tuesday, 2020-09-22

Fastnet, Force 10 by John Rousmaniere

Written shortly after the tragedy, this is a very 1970s book. The author describes himself unapologetically as a “WASP”, for example, which would probably not fly these days.

It’s long on descriptions but short on analysis. The descriptions however are pretty horrifying. If you ever feel like taking up ocean racing maybe read this first.

Friday, 2020-09-18

Re-reading Dune and Heretics of Dune

I’ve re-read Frank Herbert’s 1965 novel Dune, partly inspired by the upcoming movie.

Based on my memories I first read it in 1988 or so. The first novel in the series I read was actually Heretics of Dune (published in 1984) which I borrowed from the library in Halmstad. This must have been in 1986 or ‘87. I’ve long realized that it’s not a huge deal to read some novel series out of order - especially ones that are so self-contained as the Dune novels. Heretics takes place 5,000 years after Dune, after all.

Anyway, if you’re only going to read one Dune novel, the first one is the best. It has all the goodies - the worldbuilding, the Hero’s Journey, the tight plotting and good use of language. Even the 1960s elements have aged well - while standards like telepathy are there they’re only mentioned in passing, and the central idea of prescience is part of the plot and well handled there.

I wonder what the movie will do with the implicit connection of the Fremen with modern-day inhabitants of the Middle East. While using terms like jihad was merely a frisson in the original, they take on a darker tone in today’s climate - at least among the less enlightened. I suspect the projected 2-parter will not emphasize the jihad Paul foresees throughout the novel and instead focus on the thrilling twists and turns.

After Dune I decided to re-read Heretics. There’s almost 20 years between the novels, and it’s clear that Herbert has picked up a lot of contemporary SF tropes in the meantime. The tech in Dune is almost indistinguishable from magic - devices such as suspensors and personal shields were never explained, instead added to impart flavor - and to enforce the quasi-medieval setting of the universe.

Heretics is much more explicit in its descriptions of space travel, weapons and other technology, but not in a way that feels dated. However, the novel is marred by long stretches of interior dialogue, where the protagonists muse about religion, history, and fate in excruciating detail. While I admire Herbert for bringing in female protagonists (in the form of the Bene Gesserit sisterhood), they’re really not that interesting as characters.

I consider Dune a bona-fide SF classic and anyone interested in the genre should read it. But don’t feel pressured to read more from Herbert’s universe.

Thursday, 2020-09-17

Six months since WFH began

Monday, 2020-08-31

Friday, 2020-07-31


Hammarby Sjöstad


Jul 2019 | Jul 2018 | Jul 2017 | Jul 2016 | Jul 2015 | Jul 2014 | Jul 2013 | Jul 2012 | Jul 2011 | Jul 2010 | Jul 2009

Wednesday, 2020-07-08

Two more novels by Paul McAuley


  • War of the Maps
  • Austral

McAuley has a wide range. These books were read in reverse publication order.

War of the Maps is a far-future SF story. After our sun has become a white dwarf, post-modern humans construct a Dyson sphere around it and seed it with humans and Earth life. According to the internal legends, they play around a bit then buzz off, leaving the rest of the environment to bumble along as best they can.

The tech level is more or less Victorian but people contend with unique challenges, such as a severe lack of metallic iron and malevolent AIs buried here and here.

Austral is a near-future crime story. A genetically modified young woman gets dragged into a kidnapping plot in a post-AGW Antarctica.

Both are well worth reading!

Tuesday, 2020-06-30


Telemedecine is the only light in the darkness of COVID

This pic was supposed to be part of a pictorial depicting one day in my life during Corona, but I got bored of the concept. I just added it here so I don’t have an embarrasing gap for June 2020.

Jun 2019 | Jun 2018 | Jun 2017 | Jun 2016 | Jun 2015 | Jun 2014 | Jun 2013 | Jun 2012 | Jun 2011 | Jun 2010 | Jun 2009

Sunday, 2020-06-21

5,000 dead in Sweden