Advent of Code 2018

.. that Go only has for loops

Elm is a language which seems to compile / transpile to JavaScript

I learned how to use List.foldl/foldr in elm

How to create an infinite, repeating Sequence in Kotlin.

There is no map operator that also provides an accumulator in Kotlin (such as ReactiveX Scan)

How to read a file in JavaScript and split by line ending

That JavaScript may implicitly convert a string to a number (e.g. that 1 + "1" == "11" but 1 * "1" === 1)

How to explicitly convert a string to a number using Number("1")

That Number("") and Number(null) both are 0

That NaN !== NaN, but you have to use isNaN(NaN) instead

.. all my go projects need to go into ~/go/src, which solves the dependency link problem for go

Documentation driven development: first write the docs, then do the coding. Works great on top of test driven development!

Python has no power-assertions like groovy has. Makes testing harder 😒

VS Code and thus gitlab has a column mode for editing!

All your tests might run fine but the solution is still wrong

that it is hard to drop the imperative mindset if you are used to it too much

The zip operator in Kotlin combines two Lists into a List<Pair>>

It makes sense to return either List or Sequence from your functions depending on the result size (List or Stream in Java)

how classes work in Python

Asciidoctor lets you exclude tags in the include statement

.. structs and maps are super powerful 🤯

..go is fast 💨

Get the test input working first and assert that the results match the example

that parsing the input data is sometimes the most challenging part of these early tasks

being able to increment a non-existant integer value without checking for its existence first is super convenient

splitting strings is easier than regexing

how to create your own python modules

you can destructure in Kotlin from an Array, a List, or e Map.Entry (and probably more…​)

Kotlin’s Iterable<T>.groupingBy offers a nice way to group and then aggregate.

How to use fold with a stateful accumulator

Sometimes you spend so much time on a solution that you are afraid to start over again

I started measuring function execution performance

Once you solved a task, add asserts for your correct answers so you don’t mess up during optimization

that the elm compiler is awesome

how to effectivley use elm’s REPL

if you struggle with a problem, take a break, clear your head and get a new perspective

never assume any part of your code is too simple to have an error

pipes do not only split on new lines - also if chunks are too large

Wake up, read the task, get a rough plan while falling asleep again

Javascripts Array.splice() is blazingly fast and works in-place

Loops are costly. Knowing what you are doing can make your code faster (In this case: From 3,960 msec to 360 msec)

Get feedback! Hints from and helped cut another 60 msec

unit tests in Go feel really verbose to write (no assertions only failure checking)

writing modular/cleaner code seems to result in more loops than necessary

(again) structs and maps are profit!

graphs are fun but are super headache if you don’t have 📝 (or experience)

finally figured out that the regexp function I always need (get matches): FindStringSubmatch

you can implement a simple queue in Go using a slice and

Go has a …​ spread operator

how to define classes in JavaScript

That, even after all these years, recursion can still cause a knot in my brain

immutable data can sometimes be a burden

That it is vital to have an intuitive understanding of how the core data structures behave within a language to use them successfully

you can basically do anything with lists and dictionaries

20 years ago I learned that array modifications are slooow. Somehow I must have forgotten. Now I know again.

The JavaScript spread operator

Go unit tests need to start with func Test<Name> whereas Name needs to be capitalized, otherwise NOTHING happens 😡 rtfm

there is no asciidoctor plugin for xcode!

today’s solution part 2 is too slow to finish, but the solution already showed up after a few iterations 😎

I still seem to lack knowledge of how pointers and linked lists work; spent 3 hours implementing my own type with a bi-linked list but in practice it threw a lot of weird pointer exceptions

if you want to animate your output on the console print "\u001b[2J" clears the screen and print "\u001b[H" moves the curser to the upper left corner

if I had not rebased my codebase I could see how many hours I wasted on this 🙃

The correct syntax to assign functions to a variable is var := func (input string) bool {} (anonymous function)

You can use fmt.Scanln() to pause your program until a newline is entered. This is amazing in combination with finding of Day 13 how to reset a screen to do animations.