2016

Advent of Code 2016

Spoiler Warning: If you want to solve the challenges by yourself, don't read the code.

This directory contains the code I used to solve the challenges from Advent of Code 2016.

Contents

The following table lists the available solutions by day and language. I also added a short summary for each day. I marked the solutions which I consider especially valuable or pretty with a star (☆).

Day	Ruby	Haskell	Description	Letter Language*
01	x	x	Manhattan turtle walking	AWK
02	x		Bathroom code pad walking	Brainfuck and Ook!
03	x		(Im)possible triangles	CoffeeScript
04	x		Room checksums and encryption	C++
05			MD5 door code search	C
06	x	x	Jammed Santa repetition code	D
07	x		Swedish palindrome IPV7	Elixir
08	x		2FA display commands	Erlang
09	x		Decompress by multiply	Flow.js
10	x		Balance Bot Network	Go
11			Radiation in elevators	Hack
12	x	x	Leonardo's Monorail machine	Java
13	x		Cubicles Maze Shortest Path	Kotlin
14	x		MD5 Key search	Lisp
15	x		Kinetic disc modulus sculpture	Matlab
16	x	x	Generate Binary disk checksum	Objective-C
17	x		MD5 doors in 4x4 rooms vault	Python
18	x		Cellular tiled floor	Processing
19	x		Elves stealing White Elephants	PHP
20	x		IP range block list	Rust
21	x		Password scrambling	Scala
22	x		15-puzzle grid computing moves	TypeScipt
23	x		Safe cracking machine	Visual Basic
24	x		Duct round trips	Wolfram Language
25	x		Clock signal in assembunny	Zsh
Σ	23	4		* coming soon

Takeaways

In addition to having a lot of fun solving the puzzles, I also learned some interesting programming techniques:

• Writing programs in a language named Brainfuck
• Creating a debugger/IDE thingy using flow and React for Brainfuck with CI testing
• Pointer and value semantics in C structs
• Making a script runnable via rspec or ruby
• Global methods in Ruby
• Speed and languages: Day 12 has fast (3s) Haskell solution, which is slow through runhaskell (350s), a long and fast (<1s) Java solution and a Ruby solution in between (15s). However, building a C program with AWK and compiling builds the solution instantly.
• Optimizing a Ruby script: MD5ing in day 14 runs 80s, with fork parallelism 40s, with critical paths in C 13s, with both 5s.
• Optimizing a Crystal program: MD5ing in day 14 runs 40s, with OpenSSL's md5 20s (using ugly Pointers does not help), with fork parallelism 8s, but compiling takes an additional 11s.
• Optimizing a Scala program: MD5ing in day 14 ran 740s with a md5 found on StackOverflow, with a better formatter 166s and 46s with a specialized formatter.
• Ruby 2.4.0 was released at the end of AoC: The new hash improvements were not noticeable in Day 14's script. But the new Array#sum method (see 0424ecbb2d37b68f007bb1e44005de79ed7c9ef3) and the new Regex#match? were already useful.

Leaderboard

This year I sometimes tried to get on the daily leaderboard. And indeed I managed to get there on 4 days 1, 6, 8 and 11 scoring a total of 184 points. If the overall leaderboard was longer I'd have position 272 of about 1300 people who completed the puzzle or 13k who started it.

Other solutions

I enjoy looking at how other coder solved the riddles. This year I followed (A-Z):

• bildzeitung (Python)
• cschell (Elixir)
• fdlk (Scala)
• glguy (Haskell)
• msullivan (Haskell, Python)
• Pyrobolser (C#)