10 Lessons Learned Working on a Side Project

So I officially have RCFC 1.0 released (the phone app and the Python library). I’m really happy with how it turned out, and I wanted to share some of the lessons I learned along the way.

Lesson #0: Know your reasons for working on the side project

It is very important to be honest with yourself before you work on a project.  Why do you wan to work on it?  There are many motivators, be it money, fame, or experience, but be clear with yourself.  For me, I wanted to see if I could solve a problem, but I treated this as a learning project.  It was okay if I failed.  I wasn’t planning on making money with it.  I also wanted to see if I could build a reusable framework that others could learn from.  I wanted to know how to build a phone app.  I also was working on learning circuit design, and I needed a motivation to learn.  This is why I worked on RCFC.

Additionally, recognize your constraints.  You will not have a lot of time to work on a side project.  So I wanted to put in some upfront effort to minimize ongoing maintenance.  With RCFC, that meant that in order to update functionality, I only had to write a Python function, not update a web framework or phone app (Hooray open closed principle).

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The Release of RCFC

I’ve done it!  I’ve released my first PyPI package!  pypi_release

RCFC is a remote control for computers.  The basic idea is that I want to be able to write some Python functions, and then have a UI that can call those functions.  As I change the code, no UI changes required, it’s all generated dynamically.

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Advent Of Code 2016 Day 21 (PHP)

Advent of Code 2016 Day 20 (F#)
Advent of Code 2016 – Day 19 (Swift)

Advent of Code 2016 Day 18 (Bash)

Advent of Code 2016 Day 17 (Ruby)

Advent of Code 2016 Day 16 (Scala)

Advent of Code 2016 Day 15 (Typescript)

Advent of Code 2016 Day 14 (Go)

Advent of Code 2016 Day 13 (Lua)
Advent of Code 2016 Day 12 (C#)
Advent of Code 2016 Day 11 (Groovy)

Advent of Code 2016 Day 10 (OcaML)

Advent of Code 2016 Day 9 (Factor)

Advent of Code 2016 Day 8 (c++)
Advent of Code 2016 Day 7 (Javascript)
Advent of Code 2016 – Day 6 (Julia)
Advent of Code 2016 – Day 5( Java 8)

Advent of Code 2016 – Day 4 (Perl 6)

Advent of Code 2016 – Day 3 (Clojure)
Advent of Code – Day 2 (Python 3)
Advent Of Code 2016 – Day 1(Haskell)

Day 20

Start: 1/6/2016

Finish 1/7/2017

Language: PHP

SPOILER ALERT: If you have any inkling, any whatsoever, to work on the Advent of Code…. DO NOT READ THIS BLOG POST.  DO NOT LOOK AT MY GITHUB PROJECT.  It is no fun if you’re not solving it yourself, and you’ll feel so much better about yourself if you can figure it out without looking up an answer.  This blog post is not to give away the answer, but instead, is there for people to learn from.

As always, the following code is in my GitHub: https://github.com/pviafore/AdventOfCode2016

The Challenge

This challenge was to take a string, and apply a series of transformations on it (Swapping letters, rotating, reversing, etc.)

My idea was to keep an array where the head pointer moves around based on rotations, and operating based on that (similar to the idea of a circular array)

 

Part 1

Code Code Code ……


<?php

$head = 0;
$arr = array("a", "b", "c", "d", "e", "f", "g", "h");

function convertIndex($index){
    global $arr, $head;
    $newIndex = $index+$head;
    while($newIndex < 0){
        $newIndex += sizeof($arr);
    }
    return  $newIndex%sizeof($arr);
}
function getCharAt($index)
{
    global $arr, $head;
    $newIndex =convertIndex($index);
    return $arr[$newIndex];
}

function setCharAt($index, $value)
{
    global $arr, $head;
    $arr[convertIndex($index)] = $value;
}

function swapPos($pos1, $pos2) {
    $tmp1 = getCharAt($pos1);
    $tmp2 = getCharAt($pos2);
    setCharAt($pos1, $tmp2);
    setCharAt($pos2, $tmp1);
}

function swapLetters($letter1, $letter2) {
    global $arr;
    $index1 = array_search($letter1, $arr);
    $index2 = array_search($letter2, $arr);
    $arr[$index2] = $letter1;
    $arr[$index1] = $letter2;
}

function reverse($pos1, $pos2) {
    for ($i = $pos1, $j=$pos2; $i < $j; $i++, $j--){
        swapPos($i, $j);
    }
}

function printArray() {
    global $arr;
    for ($i = 0; $i < sizeof($arr); $i++){
        echo getCharAt($i);
    }
    echo "\n";
}

function rotateLeft($steps)
{
    global $head;
    $head += $steps;
}

function rotateRight($steps)
{
    global $head;
    $head -= $steps;
}

function move($from, $to) {
    global $arr;
    
    if ($to =$to; $i--){ 
            $newChar = getCharAt($i);
            setCharAt($i, $char);
            setCharAt($i+1, $newChar);
        }
    }
    else {
        $char = getCharAt($from);
        for ($i = $from+1; $i<=$to; $i++){ 
            $newChar = getCharAt($i);
            setCharAt($i, $char);
            setCharAt($i-1, $newChar);
        }
    }
}

function rotatePos($letter) {
    global $arr, $head;
    $index = 0;
    for ($i = 0; $i = 4) {
        $index += 1;
    }
    rotateRight($index+1);
}

function getLines() {
    $f = fopen("../day21.txt", "r");
    $lines = array();
    while (($buffer = fgets($f)) !== false) {
        $lines[] = trim($buffer);
    }
    fclose($f);
    return $lines;
}

function processLine($line) {
    $words = explode(" ", $line);
    if($words[0] == "swap" && $words[1] =="position"){
        swapPos($words[2], $words[5]);
    }
    if($words[0] == "swap" && $words[1] =="letter"){
        swapLetters($words[2], $words[5]);
    }
    if($words[0] == "rotate" && $words[1] =="left"){
        rotateLeft($words[2]);
    }
    if($words[0] == "rotate" && $words[1] =="right"){
        rotateRight($words[2]);
    }
    if($words[0] == "rotate" && $words[1] =="based"){
        rotatePos($words[6]);
    }
    if($words[0] == "reverse"){
        reverse($words[2], $words[4]);
    }
    if($words[0] == "move"){
        move($words[2], $words[5]);
    }
}


$lines = getLines();
foreach($lines as $line){   
    processLine($line);
}
printArray();
?>

This was my first foray in PHP in quite some time.  It was a bit more verbose than I remembered, but I still got this one relatively easy.

The main loop was easy, as it mostly took things line by line by line, and then chose a transformation based on the text.

Most transformations are straight forward.  I keep a global array and head pointer, along with a way to convert indices, get characters and set characters in the array.


$head = 0;
$arr = array("a", "b", "c", "d", "e", "f", "g", "h");

function convertIndex($index){
    global $arr, $head;
    $newIndex = $index+$head;
    while($newIndex < 0){
        $newIndex += sizeof($arr);
    }
    return  $newIndex%sizeof($arr);
}
function getCharAt($index)
{
    global $arr, $head;
    $newIndex =convertIndex($index);
    return $arr[$newIndex];
}

function setCharAt($index, $value)
{
    global $arr, $head;
    $arr[convertIndex($index)] = $value;
}

Swapping based on positions and swapping based on letters are pretty straight forward



function swapPos($pos1, $pos2) {
    $tmp1 = getCharAt($pos1);
    $tmp2 = getCharAt($pos2);
    setCharAt($pos1, $tmp2);
    setCharAt($pos2, $tmp1);
}

function swapLetters($letter1, $letter2) {
    global $arr;
    $index1 = array_search($letter1, $arr);
    $index2 = array_search($letter2, $arr);
    $arr[$index2] = $letter1;
    $arr[$index1] = $letter2;
}

Reversing and Rotating were also pretty easy.


function reverse($pos1, $pos2) {
    for ($i = $pos1, $j=$pos2; $i < $j; $i++, $j--){
        swapPos($i, $j);
    }
}

function rotateLeft($steps)
{
    global $head;
    $head += $steps;
}

function rotateRight($steps)
{
    global $head;
    $head -= $steps;
}

Once we get into moving (removing from one index and inserting in the other index), it took me a little while longer to get this.  I treat moving differently based on which direction I’m going to, and then I effectively “bubble” the values to the appropriate position.  I originally tried to do array slicing and recombining, but my wonky index recalculations made it tricky.


function move($from, $to) {
    global $arr;
    
    if ($to =$to; $i--){ 
            $newChar = getCharAt($i);
            setCharAt($i, $char);
            setCharAt($i+1, $newChar);
        }
    }
    else {
        $char = getCharAt($from);
        for ($i = $from+1; $i<=$to; $i++){ 
            $newChar = getCharAt($i);
            setCharAt($i, $char);
            setCharAt($i-1, $newChar);
        }
    }
}

Lastly, I worked on the rotate based on the position of a letter.  I pretty much searched for the letter in my array, then figured out how many rotations needed to happen.


function rotatePos($letter) {
    global $arr, $head;
    $index = 0;
    for ($i = 0; $i = 4) {
        $index += 1;
    }
    rotateRight($index+1);
}

 

Part 2

This part was to unscramble a password rather than scramble a password.  I reversed the lines of code, and reversed the relevant sections (such as rotating left when the command is rotate right)


function processLine($line) {
    $words = explode(" ", $line);
    if($words[0] == "swap" && $words[1] =="position"){
        swapPos($words[2], $words[5]);
    }
    if($words[0] == "swap" && $words[1] =="letter"){
        swapLetters($words[2], $words[5]);
    }
    if($words[0] == "rotate" && $words[1] =="left"){
        rotateRight($words[2]);
    }
    if($words[0] == "rotate" && $words[1] =="right"){
        rotateLeft($words[2]);
    }
    if($words[0] == "rotate" && $words[1] =="based"){
        rotatePos($words[6]);
    }
    if($words[0] == "reverse"){
        reverse($words[2], $words[4]);
    }
    if($words[0] == "move"){
        move($words[5], $words[2]);
    }
}

The tricky part of this one was figuring out how the rotate based on the position of a letter was handled.  Based on some pen and paper calculations, I found a way to derive how many rotations were needed to get to the next password


function rotatePos($letter) {
    global $arr, $head;
    $index = 0;
    for ($i = 0; $i < sizeof($arr); $i++){
        if (getCharAt($i) == $letter) {
            $index = $i;
            break;
        }
    }
    $numRotations=0;
    for ($j = 0; $j < sizeof($arr); $j++) {
        if ($j = 4 && ($j + $j + 2) % sizeof($arr) == $index) {
            $numRotations = $j+2;
            break;
        }
    }
    rotateLeft($numRotations);
}

 

Wrap-up

I had a lot of stupid mistakes in my part 2.  I kept not thinking through the problem.  Also PHP’s verbosity was weighing me down.  I felt like the array functions were clunky, and my code endd up all over the place.

I give myself a B- on this one.  I could have done better, and thought through the problems better.  My PHP code isn’t great either, so I wasn’t satisfied with this, but it’s better than some other ones.

Next up, is Day 22 with Elm.

 

Advent of Code 2016 Day 20 (F#)

Advent of Code 2016 – Day 19 (Swift)
Advent of Code 2016 Day 18 (Bash)

Advent of Code 2016 Day 17 (Ruby)

Advent of Code 2016 Day 16 (Scala)

Advent of Code 2016 Day 15 (Typescript)

Advent of Code 2016 Day 14 (Go)

Advent of Code 2016 Day 13 (Lua)
Advent of Code 2016 Day 12 (C#)
Advent of Code 2016 Day 11 (Groovy)

Advent of Code 2016 Day 10 (OcaML)

Advent of Code 2016 Day 9 (Factor)

Advent of Code 2016 Day 8 (c++)
Advent of Code 2016 Day 7 (Javascript)
Advent of Code 2016 – Day 6 (Julia)
Advent of Code 2016 – Day 5( Java 8)

Advent of Code 2016 – Day 4 (Perl 6)

Advent of Code 2016 – Day 3 (Clojure)
Advent of Code – Day 2 (Python 3)
Advent Of Code 2016 – Day 1(Haskell)

Day 20

Start: 12/26/2016

Finish 1/6/2017

Language: F#

SPOILER ALERT: If you have any inkling, any whatsoever, to work on the Advent of Code…. DO NOT READ THIS BLOG POST.  DO NOT LOOK AT MY GITHUB PROJECT.  It is no fun if you’re not solving it yourself, and you’ll feel so much better about yourself if you can figure it out without looking up an answer.  This blog post is not to give away the answer, but instead, is there for people to learn from.

As always, the following code is in my GitHub: https://github.com/pviafore/AdventOfCode2016

The Challenge

This challenge wasn’t too bad at first glance.  Given a list of blacklisted ranges of IP addresses, find the first IP address not in a blacklist.  I decided to give F# a go with this.  After OcaML didn’t go so well, I was determined to use my lessons learned and write some better code.

There was a long delay on this one due to Christmas, and a vacation in between, so I definitely missed my goal of 25 languages in 25 days.  But let’s see how far I can go.

Part 1

As usual, code first.


open System

let readlines  = System.IO.File.ReadAllLines("../day20.txt")
let toInts arr =  Seq.map uint32 arr
let getFilterFunction range =  (fun x -> x  (Seq.last range))
let uintRange = seq { System.UInt32.MinValue..System.UInt32.MaxValue} 
let allFiltersPass (filters:seqbool)>) (num:UInt32) = Seq.forall (fun f -> (f num)) filters
let skipIfOutOfRange filterFuncs = uintRange |> Seq.skipWhile (fun x -> (not (allFiltersPass filterFuncs x)) )

[]
let main argv = 
        Seq.toArray readlines 
        |> Seq.map (fun x -> x.Split[|'-'|])
        |> Seq.map toInts
        |> Seq.map getFilterFunction
        |> skipIfOutOfRange
        |> Seq.head
        |> printfn "%d"
        0


This wasn’t too bad, as I read and sanitize the input to be integers.  Then I just start iterating through numbers from 0 to MAX_INT until I find one that doesn’t fit within all the functions

Part 2

Part 2 is much tougher.  Instead of finding the first non-blacklisted IPs, we needed a count of all non-blacklisted IPs.

The basic idea was to start at zero, and then find the first number that is not in a blacklisted range.  Then find the next number that is a range and subtract the difference.  Add that difference to the sum, and start again with the ranges that are left.

First, I had to implement a solve method to do the basic checking


let rec solve num accum  ranges = 
        let matching = (getFiltersMatching num ranges)
        let remainingRanges = (getRemainingRanges ranges num)
        match Seq.isEmpty matching with
        | true ->
            match (Seq.isEmpty remainingRanges) with
            | true -> accum + (System.UInt32.MaxValue - num) + 1u
            | false -> 
                let invalidNumber = (getFirstInvalidNumber remainingRanges)
                let diff = invalidNumber - num
                solve (getNextStartingNumber (invalidNumber+1u) remainingRanges) (accum + diff) remainingRanges
        | false ->     
            let lastValid = (getLastValidNumber matching)
            match lastValid with
            | System.UInt32.MaxValue -> accum
            | otherwise -> solve (lastValid+1u) accum remainingRanges
       

[]
let main argv = 
        Seq.toArray readlines 
        |> Seq.map (fun x -> x.Split[|'-'|])
        |> Seq.map toInts
        |> solve 0u 0u
        |> printfn "%d"
        0

This was ugly code, to be sure.  First I check if I’m already in a range, and if I am, either I’m at the end of my int range, or I need to recursively check the number out of my current range.  If I’m currently in a number not in a range, I need to check what the next invalid number is.  I subtract my current number from the invalid number and then add it to an accumulator.

I had to write a few utility functions to find information about the ranges


let getFirstInvalidNumber ranges =
         ranges
         |> Seq.map (fun r -> (Seq.head r))
         |> Seq.min

let getNextStartingNumber num ranges = 
        getFiltersMatching num ranges
        |> Seq.map (fun r -> (Seq.last r))
        |> Seq.filter (fun x -> x >= num)
        |> Seq.min

let isNumBeforeRange num range =
        num  Seq.filter (fun r -> (isNumBeforeRange num r) )

let getLastValidNumber ranges =
         match (Seq.isEmpty ranges) with
         | false ->
                ranges
                |> Seq.map (fun r -> (Seq.last r))
                |> Seq.max
         | true -> System.UInt32.MaxValue

These were just straight forward sequence operations.

 

Wrap-up

F# did not go as smoothly as I wanted.  I got part two wrong at first, and it took me a while to write ugly code.  The documentation was great though, and Visual Studio Code was a blast to write F# in (inline type annotations? Yes, please.)  I would definitely consider F# for a .NET project over OcaML.

I give myself a C+ on this one.  I had a vacation in the middle, but I still had some time on either end that I was working on this one.

Next up, PHP.

 

Advent of Code 2016 – Day 19

Advent of Code 2016 Day 18 (Bash)
Advent of Code 2016 Day 17 (Ruby)

Advent of Code 2016 Day 16 (Scala)

Advent of Code 2016 Day 15 (Typescript)

Advent of Code 2016 Day 14 (Go)

Advent of Code 2016 Day 13 (Lua)
Advent of Code 2016 Day 12 (C#)
Advent of Code 2016 Day 11 (Groovy)

Advent of Code 2016 Day 10 (OcaML)

Advent of Code 2016 Day 9 (Factor)

Advent of Code 2016 Day 8 (c++)
Advent of Code 2016 Day 7 (Javascript)
Advent of Code 2016 – Day 6 (Julia)
Advent of Code 2016 – Day 5( Java 8)

Advent of Code 2016 – Day 4 (Perl 6)

Advent of Code 2016 – Day 3 (Clojure)
Advent of Code – Day 2 (Python 3)
Advent Of Code 2016 – Day 1(Haskell)

Day 19

Start: 12/25/2016

Finish 12/26/2016

Language: Swift

SPOILER ALERT: If you have any inkling, any whatsoever, to work on the Advent of Code…. DO NOT READ THIS BLOG POST.  DO NOT LOOK AT MY GITHUB PROJECT.  It is no fun if you’re not solving it yourself, and you’ll feel so much better about yourself if you can figure it out without looking up an answer.  This blog post is not to give away the answer, but instead, is there for people to learn from.

As always, the following code is in my GitHub: https://github.com/pviafore/AdventOfCode2016

The Challenge

So I ran into toolchain issues off the bat (just what I feared).  I knew I had a messed up Clang install on my machine, and it caused Swift to not be able to find some .so objects that it wanted.  Thankfully, I found a Docker image to build Swift in.  This was my first time working in Swift, and I enjoyed it.  I had been avoiding it since it was so Apple-oriented (and I haven’t done any Apple development before), but I was quite surprised.  It reminded me of Scala or Rust as far as syntax goes, and it was easy to write code.

This challenge was a rehash of Circle of Josephus.  A quick wiki refresher was what I needed to figure everything out.

Part 1

The code was quite simple :


func josephus(circleSize: Int, num: Int)-> Int {
    var last = 0
    for index in 2...circleSize {
        last=(last + num) % index 
    }
    return last + 1 
}

print(josephus(circleSize: 3014603, num:2))

I don’t even need to spend a whole lot of time on this.  I grabbed the recurrence relation from Wikipedia, and used dynamic programming to transform this into a simple linear loop.

g(n,k)=(g(n-1,k)+k){\bmod  n},{\text{ with }}g(1,k)=0

Part 2

Part two threw me for a loop (no pun intended).  I was fully expecting to see the number go up, but instead, the trick was that instead of every Kth person being eliminated, it was the person directly across who got eliminated.

I tried to do a bunch of mathematical induction and proofs to figure this one out, but kept getting stuck.  I had to go sleep on it, and came up with a better way.  The first person to get eliminated will be n/2 positions away from your index.

First I created a circular linked list to represent the elves in this example.


public class Node {
    var value: Int
    init(value: Int) {
        self.value = value
    }

    var next: Node? = nil
    weak var previous: Node?
}

func createList(size: Int) -> Node {
    let head:Node = Node(value: 1)
    var tail:Node = head
    for index in 2...size {
        let node = Node(value:index)
        node.previous = tail
        tail.next = node
        tail = node
    }
    head.previous = tail
    tail.next = head
    return head
}

Then, I advanced n/2 positions.  Then it was a simple pattern of who got eliminated.  If the circle size was odd, it was n/2 and then you skipped n/2 +1.  If the circle size was even, it was just n/2 (no skipping after).  Thus you get in the pattern, eliminate eliminate skip eliminate eliminate skip eliminate eliminate skip….. and so on.


func removeSelf(node: Node) -> Node {
    let nextNode = node.next!
    let previousNode = node.previous!
    previousNode.next = nextNode
    nextNode.previous = previousNode
    return nextNode
}

func josephus(circleSize: Int)-> Int {
    var list: Node = createList(size: circleSize)
    for _ in 1...circleSize/2 {
        list=list.next!
    }
    for size in stride(from: circleSize, to: 1, by: -1) {
        list = removeSelf(node:list)
        if (size % 2 == 1){
            list=list.next!
        }
    }
    return list.value
}

This got the right answer.

Wrap-up

I give myself a B+ on this.  I got to play around with Swift, and I liked it.  The compiler was helpful, and I found a lot of good examples.  I had to go look at the wiki to remember the Josephus equation, and if I didn’t recognize this as a Josephus problem, I would have been waiting a lot longer.

Next up is Day 20, using F#

Advent of Code 2016 Day 18 (Bash)

Advent of Code 2016 Day 17 (Ruby)
Advent of Code 2016 Day 16 (Scala)

Advent of Code 2016 Day 15 (Typescript)

Advent of Code 2016 Day 14 (Go)

Advent of Code 2016 Day 13 (Lua)
Advent of Code 2016 Day 12 (C#)
Advent of Code 2016 Day 11 (Groovy)

Advent of Code 2016 Day 10 (OcaML)

Advent of Code 2016 Day 9 (Factor)

Advent of Code 2016 Day 8 (c++)
Advent of Code 2016 Day 7 (Javascript)
Advent of Code 2016 – Day 6 (Julia)
Advent of Code 2016 – Day 5( Java 8)

Advent of Code 2016 – Day 4 (Perl 6)

Advent of Code 2016 – Day 3 (Clojure)
Advent of Code – Day 2 (Python 3)
Advent Of Code 2016 – Day 1(Haskell)

Day 18

Start: 12/22/2016

Finish 12/24/2016

Language: Bash

SPOILER ALERT: If you have any inkling, any whatsoever, to work on the Advent of Code…. DO NOT READ THIS BLOG POST.  DO NOT LOOK AT MY GITHUB PROJECT.  It is no fun if you’re not solving it yourself, and you’ll feel so much better about yourself if you can figure it out without looking up an answer.  This blog post is not to give away the answer, but instead, is there for people to learn from.

As always, the following code is in my GitHub: https://github.com/pviafore/AdventOfCode2016

The Challenge

 

So I started with good intentions with Forth.  Then it took me an hour to get the toolchain installed on my linux box (had to go scraping through mailing lists).  Then I spent a lot of time poring over documentation.  After a few hours of working, I couldn’t even figure out how to read a file.  Sometimes you have to know when you’re beat, and I feel like to learn Forth, I really needed a week or two and a good reference to learn it.  I much preferred Factor.

So I made the tough decision to pivot to Bash.  I figured I’d use Bash much more than Forth in my career.  It stung having to back down, but it was bound to happen.

This challenge was about figuring out which tiles were safe to step on, and you could derive the next row of tiles from the previous row.  Then you had to sum up all the safe tiles across a whole lot of rows.

Part 1

Let’s look at the code.


#!/bin/bash
target=$(<"../day18.txt")

getChar() {
    sequence=$1
    index=$2
    if [ "$index" == "-1" ]; then
        char="."
    elif [ "$index" == "${#sequence}" ]; then
        char="."
    else
        char=${sequence:$index:1}
    fi
}
getNextChar() {
    getChar $1 $(($2-1))
    char1=$char
    getChar $1 $2
    char2=$char
    getChar $1 $(($2+1))
    char3=$char
    if [[ "$char1" = "^" && "$char2" = "^" && "$char3" = "." ]]; then
        nextChar="^";
    elif [[ "$char1" = "." && "$char2" = "^" && "$char3" = "^" ]]; then
        nextChar="^";
    elif [[ "$char2" = "." && "$char1" = "." && "$char3" = "^" ]]; then
        nextChar="^";
    elif [[ "$char2" = "." && "$char3" = "." && "$char1" = "^" ]]; then
        nextChar="^";
    else   
         nextChar=".";
    fi
}

getNextSequence() {
    sequence=$1
    target=""
    for (( i=0; i<${#sequence}; i++)) 
    do
        getNextChar $sequence $i
        target=$target$nextChar
    done
}

rows=40
fullString=""
for (( j=0; j<${rows}; j++))
do
    fullString=$fullString$target
    getNextSequence $target    
done
safe="${fullString//[^.]}"
echo ${#safe}

Starting with the main loop -> We keep looping over the rows getting the next sequence, and concatenating that onto a string.  Then we loop over the string and get the only safe tiles (“.”).



rows=40
fullString=""
for (( j=0; j<${rows}; j++))
do
    fullString=$fullString$target
    getNextSequence $target    
done
safe="${fullString//[^.]}"
echo ${#safe}

The next part is figuring out what each sequence should look like.  We simply loop over the string, determining what the next character should be.   The next character is determined by a set of rules outlined in the problem (see the big four if statements comparing three characters)


getNextChar() {
    getChar $1 $(($2-1))
    char1=$char
    getChar $1 $2
    char2=$char
    getChar $1 $(($2+1))
    char3=$char
    if [[ "$char1" = "^" && "$char2" = "^" && "$char3" = "." ]]; then
        nextChar="^";
    elif [[ "$char1" = "." && "$char2" = "^" && "$char3" = "^" ]]; then
        nextChar="^";
    elif [[ "$char2" = "." && "$char1" = "." && "$char3" = "^" ]]; then
        nextChar="^";
    elif [[ "$char2" = "." && "$char3" = "." && "$char1" = "^" ]]; then
        nextChar="^";
    else   
         nextChar=".";
    fi
}

getNextSequence() {
    sequence=$1
    target=""
    for (( i=0; i<${#sequence}; i++)) 
    do
        getNextChar $sequence $i
        target=$target$nextChar
    done
}

The last part is how to get character from a string.  I wanted to wrap this in a function so that out of bounds accesses returned a safe tile (this was important due to the rules of  the problem)


getChar() {
    sequence=$1
    index=$2
    if [ "$index" == "-1" ]; then
        char="."
    elif [ "$index" == "${#sequence}" ]; then
        char="."
    else
        char=${sequence:$index:1}
    fi
}

Part 2

Part 2 made us care about 400,000.  I tried to run the same code again with a different parameter, and after 30 hours of runtime, it wasn’t getting anywhere.

I did some quick profiling using the time command and a smaller solution space size, and figured out the string concatenation was taking the long part.  So I swapped the code up a bit, and ran a count each time during the loop


rows=400000
fullString=""
count=0
for (( j=0; j<${rows}; j++))
do
    safe="${target//[^.]}"
    count=$(($count+${#safe}))
    getNextSequence $target
done
echo $count

After about an hour and a half of runtime, I finally got the right answer

 

Wrap-up

I wanted to get Forth up and going, but I was worried that it was taking too long.  Its not like Bash was that much better, but I had to do something.  The code wasn’t pretty, and it took me three days, but it’s something.  My time is running out (I didn’t think I’d get all 25 languages in 25 days, but there’s still a chance if I motor on up.

I give myself a D- on this one.  I gave up early with Forth, and only with perseverance did I go through with Bash.  I learned some stuff about Bash (knowing I don’t want to do any significant programming in it), like how it handles return values (it doesn’t) and how it handles parameters of functions.

 

Next up, I’ll be trying Swift for Day 19 (assuming I don’t run into any toolchain problems)

 

Advent of Code 2016 Day 17 (Ruby)

Advent of Code 2016 Day 16 (Scala)
Advent of Code 2016 Day 15 (Typescript)

Advent of Code 2016 Day 14 (Go)

Advent of Code 2016 Day 13 (Lua)
Advent of Code 2016 Day 12 (C#)
Advent of Code 2016 Day 11 (Groovy)

Advent of Code 2016 Day 10 (OcaML)

Advent of Code 2016 Day 9 (Factor)

Advent of Code 2016 Day 8 (c++)
Advent of Code 2016 Day 7 (Javascript)
Advent of Code 2016 – Day 6 (Julia)
Advent of Code 2016 – Day 5( Java 8)

Advent of Code 2016 – Day 4 (Perl 6)

Advent of Code 2016 – Day 3 (Clojure)
Advent of Code – Day 2 (Python 3)
Advent Of Code 2016 – Day 1(Haskell)

Day 17

Start: 12/21/2016

Finish 12/21/2016

Language: Ruby

SPOILER ALERT: If you have any inkling, any whatsoever, to work on the Advent of Code…. DO NOT READ THIS BLOG POST.  DO NOT LOOK AT MY GITHUB PROJECT.  It is no fun if you’re not solving it yourself, and you’ll feel so much better about yourself if you can figure it out without looking up an answer.  This blog post is not to give away the answer, but instead, is there for people to learn from.

As always, the following code is in my GitHub: https://github.com/pviafore/AdventOfCode2016

The Challenge

This was another find-your-way out of a maze problem, but the trick was every time you entered a room, the paths you could take changed based on the path you have already walked.  Sounded like a job for a Breadth-First Search if you ask me.

I did this one in Ruby, and I was quite pleased with it.  This was my first from-scratch program in Ruby, which is kinda embarrassing, considering I named my dog after the Ruby Programming language.  However, it came together quickly, and it was another session I was quite happy with.

 

Part 1

You know the drill, code first :


require 'digest'

input = "qljzarfv"

def is_valid_hash_character(hash, pos) 
    ('b'..'f').include? hash[pos]
end

Point = Struct.new(:x, :y) do
    def get_moves(input)
        md5 = Digest::MD5.new.update(input)
        hash = md5.hexdigest
        moves = Array.new
        moves << "U" if y != 1 and  is_valid_hash_character(hash, 0)
        moves << "D" if y != 4 and  is_valid_hash_character(hash, 1)
        moves << "L" if x != 1 and  is_valid_hash_character(hash, 2)
        moves << "R" if x != 4 and  is_valid_hash_character(hash, 3)
        moves
    end
end

def move_point(point, move)
    return Point.new(point.x, point.y-1) if move == "U"
    return Point.new(point.x, point.y+1) if move == "D"
    return Point.new(point.x-1, point.y) if move == "L"
    return Point.new(point.x+1, point.y) if move == "R"
end

def move_state(state, move)
    return State.new(move_point(state.point, move), state.passcode+move)
end

State = Struct.new(:point, :passcode) do
    def get_moves
        point.get_moves(passcode)
    end
end

states = [State.new(Point.new(1,1), input)]
while not states.empty? do
    current = states.shift
    if current.point == Point.new(4,4) then 
        puts current.passcode.slice(input.length, current.passcode.length)
        break
    end
    states = states + current.get_moves.map { |move| move_state(current, move)}
end

Not bad, about 50 lines of code.

First I created a point structure that tracked x and y coordinates, while also being able to tell you what moves were valid from where you were.



def is_valid_hash_character(hash, pos) 
    ('b'..'f').include? hash[pos]
end

Point = Struct.new(:x, :y) do
    def get_moves(input)
        md5 = Digest::MD5.new.update(input)
        hash = md5.hexdigest
        moves = Array.new
        moves << "U" if y != 1 and  is_valid_hash_character(hash, 0)
        moves << "D" if y != 4 and  is_valid_hash_character(hash, 1)
        moves << "L" if x != 1 and  is_valid_hash_character(hash, 2)
        moves << "R" if x != 4 and  is_valid_hash_character(hash, 3)
        moves
    end
end

I wanted to keep immutability high on this, so I created a helper function to move a point around.  I’ll tell you, one thing I miss in other languages is the ability to put the if statement at the end of the line (or the unless statement.


def move_point(point, move)
    return Point.new(point.x, point.y-1) if move == "U"
    return Point.new(point.x, point.y+1) if move == "D"
    return Point.new(point.x-1, point.y) if move == "L"
    return Point.new(point.x+1, point.y) if move == "R"
end

Next I wanted to keep track of state by knowing what our current passcode was and our current state (with a move function as well)


def move_state(state, move)
    return State.new(move_point(state.point, move), state.passcode+move)
end

State = Struct.new(:point, :passcode) do
    def get_moves
        point.get_moves(passcode)
    end
end

Finally, the main loop was simply popping a state off a queue, finding the next moves, and pushing all those moves onto the queue.  If I ever ended up in my goal, I’d print out my path (and since this is BFS, I’m guaranteed to find that shortest distance first).


states = [State.new(Point.new(1,1), input)]
while not states.empty? do
    current = states.shift
    if current.point == Point.new(4,4) then 
        puts current.passcode.slice(input.length, current.passcode.length)
        break
    end
    states = states + current.get_moves.map { |move| move_state(current, move)}
end

 

Part 2

Part two asked me to find the longest path that terminated at my goal.  I dreaded this at first, as I was worried some complexity would bite me, but my code still ran fast.  All Ihad to change was the main loop.  Instead of breaking when I found an answer, I would just track if it was the longest so far and continue on with my loop


states = [State.new(Point.new(1,1), input)]
longest = 0
while not states.empty? do
    current = states.shift
    if current.point == Point.new(4,4) then 
        length = current.passcode.length - input.length
        longest = [length, longest].max
    else
        states = states + current.get_moves.map { |move| move_state(current, move)}
    end
end
puts longest

Wrap-up

I give myself another A.  I’m on a roll so far, which is good, because I think the next four languages I’m going to tackle are Forth, Swift, F# and PHP, all of which are going to be interesting.  I wish I had more code in my Ruby stuff that dealt with blocks, but I got a good chance to play around with it’s expressiveness, and I like how it came together.

Next up, I’m going back to another stack-based language and will be playing with Forth for day 18.