2015

Advent of Code 2015

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 2015.

I used Haskell for most of the riddles. Sometimes I conceived a Ruby solution, if there was a neat application for regexes or OOP. For algorithms which profit from random access or are just easily faster imperatively, I used C.

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	C	Haskell	Ruby	Description
01	x	x	x	Parenthesis counting
02		x		Wrapping paper
03		x		Routes delivering to houses
04	☆			MD5 mining
05		x	x	Nice string text processing
06		x	x	Light installation
07		x		Bitwise signal wiring
08		x	x	String escaping
09		☆		TSP
10		☆		Look-and-Say Numbers / RLE
11	☆	x		Base26 increment, password rules
12		x		JSON number sums
13		x		Seating happiness
14		x	☆	Racing Reindeer
15	x	x		Optimize cookie receipt
16		x		Aunt Detective
17	x	x		Eggnog container subset sums
18		x		GoL with Lights
19		x		Medicine with molecules and grammars
20	x			Elves delivering by factor sums
21		x		Bossfight with items
22		x		Bossfight with Wizard and mana
23		x		RAM Computer Simulation
24		x		Optimizing partitions
25		x		Cantor pairing and residue field
Σ	6	23	5

Takeaways

In addition to having a lot of fun solving the puzzles, I also applied some interesting programming techniques for the first time in C or Ruby:

• Reading a file letter by letter in C, in Haksell and in Ruby.
• Using Pointer arithmetics, function pointers and calling MD5 in C.
• Some advanced Regex usage in Ruby here and here.
• Creating PNGs with Ruby.
• Doing a neat OOP simulation in Ruby.
• Comparing a naive Haskell solution with a fast C solution using DP.

Also I learned and applied these new concepts about Haskell:

• Parsec, very basicly and in complex situations
• -> as reader monad
• Regexes
• Arrays
• Stacking monad transformers
• Interpreting a very simple programming language

Completion

I finally completed all the puzzles:

Other solutions

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

• cschell (Ruby)
• darinc (many languages)
• glguy (Haskell)