https://github.com/bobbicodes/advent-2016

Advent of Code 2016
https://github.com/bobbicodes/advent-2016

Last synced: 11 months ago
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Advent of Code 2016

• Host: GitHub
• URL: https://github.com/bobbicodes/advent-2016
• Owner: bobbicodes
• Created: 2017-11-07T18:00:30.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2018-05-25T00:06:03.000Z (about 8 years ago)
• Last Synced: 2025-03-26T05:09:09.169Z (about 1 year ago)
• Language: Clojure
• Homepage:
• Size: 448 KB
• Stars: 1
• Watchers: 0
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

          
# Advent of Code 2016 problems

Since they all involve parsing some kind of input data, this will be a job for ... [Instaparse](https://github.com/Engelberg/instaparse)!

With it we can use a context-free grammar to generate a tree-like structure from our data.

### Day 4

For example, here's an input string for the day 4 problem. Each room is represented as a key, id and checksum:

    aaaaa-bbb-z-y-x-123[abxyz]

The key is made of one or more strings of letters separated with hyphens.

The id is a string of numbers, and the checksum is a string of letters in brackets.

This is how we represent that in [EBNF notation](en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form)... In Clojure!:

  

    (def room-parser

      (insta/parser

        "room = key id checksum

        key = (word )+

         = '-'

        word = #'[a-zA-Z]+'

        checksum = <'['> word <']'>

        id = #'[0-9]+'"))

        

 Now we pass the input to our shiny-new parser:

    (room-parser "aaaaa-bbb-z-y-x-123[abxyz]")

    

And we get our magical tree! Ooowee!

  

    => [:room [:key [:word "aaaaa"] [:word "bbb"] [:word "z"] [:word "y"] [:word "x"]]

    [:id "123"]

    [:checksum [:word "abxyz"]]]

We can even make a pretty little chart using [rhizome](github.com/ztellman/rhizome) and [graphviz](www.graphviz.org/)! Oooweee!

    (insta/visualize  (room-parser "aaaaa-bbb-z-y-x-123[abxyz]"))

![room](https://github.com/sdfwer124/interview-problems/blob/master/room.png)

### Day 10

Let's do another one!

Day 10 we are programming robots.

The input data consists of instructions like this:

    bot 147 gives low to bot 67 and high to bot 71

    bot 142 gives low to bot 128 and high to bot 164

    bot 47 gives low to bot 4 and high to bot 209

    bot 107 gives low to bot 194 and high to bot 103

    bot 102 gives low to bot 82 and high to bot 3

    bot 101 gives low to bot 46 and high to bot 111

    value 23 goes to bot 76

    

We'll break it down to the first line:

    (def bots "bot 147 gives low to bot 67 and high to bot 71")

    

Now we'll express the relevant data in EBNF notation: 

    (def bot-parser

      (insta/parser

        "handoff = bot+

         bot = word whitespace id

         word = #'[a-zA-Z]+'

         whitespace = #'\\s+'

         id = #'[0-9]+'"))

         

  Each transaction performed by the bots is represented as a "handoff".

  A handoff is a messenger bot followed by one or more receiver bots.

  

  Let's use this parser to visualize this transaction:

  

    (insta/visualize (bot-parser bots))

    

![bots](https://github.com/sdfwer124/interview-problems/blob/master/src/advent/bots.png)