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<title>Personal Projects</title>
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<a style="text-decoration: none;" href="index.html"><--</a>
<h2>Personal Projects</h2>
<h3>Synacor Challenge</h3>
After participating in <a href="https://adventofcode.com" target="_blank">Advent of Code</a>
for a few years now, I have grown a fan of Eric Wastl's puzzles. This
is a multi-part challenge that involves implementing a virtual machine
to interpret and run the supplied binary file. You are also given a
document outlining the <a href="https://raw.githubusercontent.com/waffle87/synacor_challenge/master/arch-spec" target="_blank">architecture specification</a>
of the machine that can run the binary file. Once completed and the self-tests
are passed, you're taken on text-based adventure as the program runs, that is very similar
to AoC stories. The goal is to find 8 codes while completing various puzzles in
the program. Before the original <a href="https://challenge.synacor.com" target="_blank">site</a>
was taken down (pretty sure Eric doesn't work at Synacor anymore), you could validate the
codes found on the site, but since it is no longer up, The codes can be manually verified.
Thanks to <a href="https://github.com/Aneurysm9/vm_challenge" target="_blank">Aneurysm9/vm_challenge</a>
for providing a binary file and matching checksums for the codes. I wrote a <a href="https://github.com/waffle87/synacor_challenge/blob/master/tools/validate.py" target="_blank">small script</a>
to validate them from a text file. I chose to implement my solution in C with a simple stack
data structure, as that seems most fitting for the task at hand. My implementation and related tools can
be found <a href="https://github.com/waffle87/synacor_challenge" target="_blank">here</a>
for those interested. The rest of what's here is likely to be spoilers...
<h4>Code 1</h4>
This one is found in plain text in the <code>arch-spec</code> file.
<pre>
== hints ==
- Start with operations 0, 19, and 21.
- Here's a code for the challenge website: <CODE>
</pre>
<h4>Code 2</h4>
After implementing a basic interpreter that supports the first subset of
opcodes (<code>out</code>, <code>noop</code>, and <code>halt</code>), this one is found in the output.
<pre>
Welcome to the Synacor OSCON 2012 Challenge!
Please record your progress by putting codes like
this one into the challenge website: <CODE>
</pre>
Just for fun, this one can also be spotted early on in the hexdump of the binary file:
<pre>
00000210 13 00 20 00 13 00 49 00 13 00 6d 00 13 00 6f 00 |.. ...I...m...o.|
00000220 13 00 46 00 13 00 7a 00 13 00 74 00 13 00 57 00 |..F...z...t...W.|
00000230 13 00 51 00 13 00 43 00 13 00 76 00 13 00 78 00 |..Q...C...v...x.|
00000240 13 00 6a 00 13 00 0a 00 13 00 0a 00 13 00 45 00 |..j.............|
</pre>
<h4>Code 3</h4>
To retrieve this code, the interpreter must be fully implemented and must
pass the initial self-tests. If those conditions are met, the third code
is printed.
<pre>
Executing self-test...
self-test complete, all tests pass
The self-test completion code is: <CODE>
</pre>
<h4>Code 4</h4>
Now, the adventure aspect of the challenge begins. Pay attention to the things
of interest, and <code>take</code>/<code>use</code> them as needed, like the
tablet here.
<pre>
What do you do?
take tablet
Taken.
What do you do?
use tablet
You find yourself writing <CODE> on the tablet. Perhaps it's some
kind of code?
</pre>
<h4>Code 5</h4>
This puzzle appears to be a maze after several entries of south, north,
west, etc. I decided to map my steps with pen and paper. After not too
long, I arrive at the next code, but not without getting lost and
eaten by grues numerous times.
<pre>
What do you do?
east
Chiseled on the wall of one of the passageways, you see:
<CODE>
</pre>
<h4>Code 6</h4>
The next puzzle is a maths problem. There will be some coins each with
a numeric value that you can inspect to see. The coins must be arranged
in a specific order to satisfy the equation on the wall.
<pre>
There is a strange monument in the center of the hall with circular slots and unusual symbols. It reads:
_ + _ * _^2 + _^3 - _ = 399
</pre>
<ul>
<li>Red coin: 2</li>
<li>Blue coin: 9</li>
<li>Shiny coin: 5</li>
<li>Concave coin: 7</li>
<li>Corroded coin: 3</li>
</ul>
This is easy enough to be by hand, but why not make another <a href="https://github.com/waffle87/synacor_challenge/blob/master/tools/coin.py" target="_blank">script</a>
to do it. Looks like <code>9 + 2*5^2 + 7^3 - 3 = 399</code>
will do it, so arrange the coins in order blue, red, shiny, concave, corroded.
After completing this, a previously locked door opens and our next code is revealed.
<pre>
What do you do?
use teleporter
You activate the teleporter! As you spiral through time and space, you think you see a pattern in the stars...
<CODE>
</pre>
<h4>Code 7</h4>
This is by far the most clever puzzle in this challenge. There's a
strange book that contains some information about using the teleporter.
Some provision to log instructions and register values is crucial
for this puzzle. It appears we must set the 8th register to a certain
value. We can set the register to a non-zero value to progress in the
program, but it will not provide the correct code, thus we need to find
the correct value. The underlying algorithm is a variation of the <a href="https://en.wikipedia.org/wiki/Ackermann_function" target="_blank">Ackermann function</a>.
The modified function can be found in the <a href="https://github.com/waffle87/synacor_challenge/blob/master/tools/ackermann.c" target="_blank">program</a>
used to find the register value. Python proved to be a bit too slow to compute this.
Once set to the correct value (25734 in my case), the seventh code is shown.
<pre>
You wake up on a sandy beach with a slight headache. The last thing you remember is activating that teleporter... but now you can't find it anywhere in your pack. Someone seems to have drawn a message in the sand here:
<CODE>
It begins to rain. The message washes away. You take a deep breath and feel firmly grounded in reality as the effects of the teleportation wear off.
</pre>
<h4>Code 8</h4>
This looks to be some sort of arrangement of tiles, each with a
number of arithmetic operation. By moving from one tile to another,
you are constructing an expression that must evaluate to the number
on the door: 30. This is a BFS application to construct the shortest
path to the door. I made another <a href="https://github.com/waffle87/synacor_challenge/blob/master/tools/orb_maze.py" target="_blank">script</a>
to achieve this. After inputting the appropriate cardinal directions,
we see the final code in a mirror. Of course, it is entered in reverse.
<pre>
You gaze into the mirror, and you see yourself gazing back.
But wait!
It looks like someone wrote on your face while you were unconscious on the beach!
Through the mirror, you see <CODE> scrawled in charcoal on your forehead.
Congratulations; you have reached the end of the challenge!
</pre>
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