-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathindex.html
321 lines (303 loc) · 12.7 KB
/
index.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<!-- 2022-12-22 Thu 14:10 -->
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<title>🎄🖥 Core Retro 210: Advent of Code 🖥🎄</title>
<meta name="author" content="Neil Forrest" />
<meta name="generator" content="Org Mode" />
<style>
#content { max-width: 60em; margin: auto; }
.title { text-align: center;
margin-bottom: .2em; }
.subtitle { text-align: center;
font-size: medium;
font-weight: bold;
margin-top:0; }
.todo { font-family: monospace; color: red; }
.done { font-family: monospace; color: green; }
.priority { font-family: monospace; color: orange; }
.tag { background-color: #eee; font-family: monospace;
padding: 2px; font-size: 80%; font-weight: normal; }
.timestamp { color: #bebebe; }
.timestamp-kwd { color: #5f9ea0; }
.org-right { margin-left: auto; margin-right: 0px; text-align: right; }
.org-left { margin-left: 0px; margin-right: auto; text-align: left; }
.org-center { margin-left: auto; margin-right: auto; text-align: center; }
.underline { text-decoration: underline; }
#postamble p, #preamble p { font-size: 90%; margin: .2em; }
p.verse { margin-left: 3%; }
pre {
border: 1px solid #e6e6e6;
border-radius: 3px;
background-color: #f2f2f2;
padding: 8pt;
font-family: monospace;
overflow: auto;
margin: 1.2em;
}
pre.src {
position: relative;
overflow: auto;
}
pre.src:before {
display: none;
position: absolute;
top: -8px;
right: 12px;
padding: 3px;
color: #555;
background-color: #f2f2f299;
}
pre.src:hover:before { display: inline; margin-top: 14px;}
/* Languages per Org manual */
pre.src-asymptote:before { content: 'Asymptote'; }
pre.src-awk:before { content: 'Awk'; }
pre.src-authinfo::before { content: 'Authinfo'; }
pre.src-C:before { content: 'C'; }
/* pre.src-C++ doesn't work in CSS */
pre.src-clojure:before { content: 'Clojure'; }
pre.src-css:before { content: 'CSS'; }
pre.src-D:before { content: 'D'; }
pre.src-ditaa:before { content: 'ditaa'; }
pre.src-dot:before { content: 'Graphviz'; }
pre.src-calc:before { content: 'Emacs Calc'; }
pre.src-emacs-lisp:before { content: 'Emacs Lisp'; }
pre.src-fortran:before { content: 'Fortran'; }
pre.src-gnuplot:before { content: 'gnuplot'; }
pre.src-haskell:before { content: 'Haskell'; }
pre.src-hledger:before { content: 'hledger'; }
pre.src-java:before { content: 'Java'; }
pre.src-js:before { content: 'Javascript'; }
pre.src-latex:before { content: 'LaTeX'; }
pre.src-ledger:before { content: 'Ledger'; }
pre.src-lisp:before { content: 'Lisp'; }
pre.src-lilypond:before { content: 'Lilypond'; }
pre.src-lua:before { content: 'Lua'; }
pre.src-matlab:before { content: 'MATLAB'; }
pre.src-mscgen:before { content: 'Mscgen'; }
pre.src-ocaml:before { content: 'Objective Caml'; }
pre.src-octave:before { content: 'Octave'; }
pre.src-org:before { content: 'Org mode'; }
pre.src-oz:before { content: 'OZ'; }
pre.src-plantuml:before { content: 'Plantuml'; }
pre.src-processing:before { content: 'Processing.js'; }
pre.src-python:before { content: 'Python'; }
pre.src-R:before { content: 'R'; }
pre.src-ruby:before { content: 'Ruby'; }
pre.src-sass:before { content: 'Sass'; }
pre.src-scheme:before { content: 'Scheme'; }
pre.src-screen:before { content: 'Gnu Screen'; }
pre.src-sed:before { content: 'Sed'; }
pre.src-sh:before { content: 'shell'; }
pre.src-sql:before { content: 'SQL'; }
pre.src-sqlite:before { content: 'SQLite'; }
/* additional languages in org.el's org-babel-load-languages alist */
pre.src-forth:before { content: 'Forth'; }
pre.src-io:before { content: 'IO'; }
pre.src-J:before { content: 'J'; }
pre.src-makefile:before { content: 'Makefile'; }
pre.src-maxima:before { content: 'Maxima'; }
pre.src-perl:before { content: 'Perl'; }
pre.src-picolisp:before { content: 'Pico Lisp'; }
pre.src-scala:before { content: 'Scala'; }
pre.src-shell:before { content: 'Shell Script'; }
pre.src-ebnf2ps:before { content: 'ebfn2ps'; }
/* additional language identifiers per "defun org-babel-execute"
in ob-*.el */
pre.src-cpp:before { content: 'C++'; }
pre.src-abc:before { content: 'ABC'; }
pre.src-coq:before { content: 'Coq'; }
pre.src-groovy:before { content: 'Groovy'; }
/* additional language identifiers from org-babel-shell-names in
ob-shell.el: ob-shell is the only babel language using a lambda to put
the execution function name together. */
pre.src-bash:before { content: 'bash'; }
pre.src-csh:before { content: 'csh'; }
pre.src-ash:before { content: 'ash'; }
pre.src-dash:before { content: 'dash'; }
pre.src-ksh:before { content: 'ksh'; }
pre.src-mksh:before { content: 'mksh'; }
pre.src-posh:before { content: 'posh'; }
/* Additional Emacs modes also supported by the LaTeX listings package */
pre.src-ada:before { content: 'Ada'; }
pre.src-asm:before { content: 'Assembler'; }
pre.src-caml:before { content: 'Caml'; }
pre.src-delphi:before { content: 'Delphi'; }
pre.src-html:before { content: 'HTML'; }
pre.src-idl:before { content: 'IDL'; }
pre.src-mercury:before { content: 'Mercury'; }
pre.src-metapost:before { content: 'MetaPost'; }
pre.src-modula-2:before { content: 'Modula-2'; }
pre.src-pascal:before { content: 'Pascal'; }
pre.src-ps:before { content: 'PostScript'; }
pre.src-prolog:before { content: 'Prolog'; }
pre.src-simula:before { content: 'Simula'; }
pre.src-tcl:before { content: 'tcl'; }
pre.src-tex:before { content: 'TeX'; }
pre.src-plain-tex:before { content: 'Plain TeX'; }
pre.src-verilog:before { content: 'Verilog'; }
pre.src-vhdl:before { content: 'VHDL'; }
pre.src-xml:before { content: 'XML'; }
pre.src-nxml:before { content: 'XML'; }
/* add a generic configuration mode; LaTeX export needs an additional
(add-to-list 'org-latex-listings-langs '(conf " ")) in .emacs */
pre.src-conf:before { content: 'Configuration File'; }
table { border-collapse:collapse; }
caption.t-above { caption-side: top; }
caption.t-bottom { caption-side: bottom; }
td, th { vertical-align:top; }
th.org-right { text-align: center; }
th.org-left { text-align: center; }
th.org-center { text-align: center; }
td.org-right { text-align: right; }
td.org-left { text-align: left; }
td.org-center { text-align: center; }
dt { font-weight: bold; }
.footpara { display: inline; }
.footdef { margin-bottom: 1em; }
.figure { padding: 1em; }
.figure p { text-align: center; }
.equation-container {
display: table;
text-align: center;
width: 100%;
}
.equation {
vertical-align: middle;
}
.equation-label {
display: table-cell;
text-align: right;
vertical-align: middle;
}
.inlinetask {
padding: 10px;
border: 2px solid gray;
margin: 10px;
background: #ffffcc;
}
#org-div-home-and-up
{ text-align: right; font-size: 70%; white-space: nowrap; }
textarea { overflow-x: auto; }
.linenr { font-size: smaller }
.code-highlighted { background-color: #ffff00; }
.org-info-js_info-navigation { border-style: none; }
#org-info-js_console-label
{ font-size: 10px; font-weight: bold; white-space: nowrap; }
.org-info-js_search-highlight
{ background-color: #ffff00; color: #000000; font-weight: bold; }
.org-svg { }
</style>
</head>
<body>
<div id="content" class="content">
<h1 class="title">🎄🖥 Core Retro 210: Advent of Code 🖥🎄</h1>
<div id="table-of-contents" role="doc-toc">
<h2>Table of Contents</h2>
<div id="text-table-of-contents" role="doc-toc">
<ul>
<li><a href="#org0b59348">1. Background</a></li>
<li><a href="#org78e51d7">2. The idea</a></li>
<li><a href="#org19e64e2">3. Problem: Part 1</a></li>
<li><a href="#org148a76a">4. Problem: Part 2</a></li>
</ul>
</div>
</div>
<div id="outline-container-org0b59348" class="outline-2">
<h2 id="org0b59348"><span class="section-number-2">1.</span> Background</h2>
<div class="outline-text-2" id="text-1">
<ul class="org-ul">
<li><a href="https://adventofcode.com/2022">Advent of Code</a> is an advent calendar of programming puzzles created by Eric Wastl</li>
<li>Each day in December there is a two part puzzle presented in the context of a Christmas themed story</li>
<li>The answers can be found by creating a program (in any language) to process a unique textual “puzzle input”</li>
<li>The output of the program (usually numerical, or a short string) can be exchanged for points</li>
</ul>
</div>
</div>
<div id="outline-container-org78e51d7" class="outline-2">
<h2 id="org78e51d7"><span class="section-number-2">2.</span> The idea</h2>
<div class="outline-text-2" id="text-2">
<ul class="org-ul">
<li>This is fun; but being purely text based has its limitations</li>
<li>Being graphics developers we should be able to do better - let’s try!</li>
</ul>
</div>
</div>
<div id="outline-container-org19e64e2" class="outline-2">
<h2 id="org19e64e2"><span class="section-number-2">3.</span> Problem: Part 1</h2>
<div class="outline-text-2" id="text-3">
<p>
It’s late on Christmas Eve. You are relaxing with the elves at the North Pole. Everyone is exhausted from the last minute push to meet the Christmas deadlines but there’s still a low key a party atmosphere developing amongst the elves. Santa left several hours ago and is no doubt at this very moment squeezing his hefty frame down yet another inadequately sized chimney in the line of duty.
</p>
<p>
Just as you are about to pour yourself another sickly eggnog that elves seem so fond of… You receive an urgent message from Santa on your communications device. In your excitement you accidentally spill your sticky raw egg based beverage all over the primitive device. When you look at the screen you find to your horror that the device is malfunctioning. The message (an image and your <b>puzzle input</b>) is visible on the screen, but the device is unable to decipher Santa’s top secret encryption algorithm and as such the image is completely unintelligible.
</p>
<p>
The text below the image reads:
</p>
<blockquote>
<p>
“URGENT: I’ve just found this Christmas letter from Neil down the side of the seat in the sleigh, I must have missed it before. Please send me this gift ASAP! We don’t have long until morning.”
</p>
</blockquote>
<div id="org97d67e0" class="figure">
<p><img src="images/encoded.png" alt="encoded.png" />
</p>
</div>
<p>
You’ll need to decode the message yourself to discover what Christmas gift Neil wanted.
</p>
<p>
Luckily you overheard the elves discussing how Santa’s device encodes images.
</p>
<p>
The encoded image is a PNG file with 4 8-bit channels: RGBA. So each pixel has 4 values between 0-255.
</p>
<ol class="org-ol">
<li>A random key is generated and is stored in the alpha channel of the image</li>
<li>The RGB channels of the original image are combined with the key in the A channel to encrypt them in the following way:
<ol class="org-ol">
<li>For the RED channel, the key is multiplied by 100 before being added to the original value, i.e.: <code>encoded.r = orig.r + 100*orig.a</code>. If the result is bigger that 255, then it wraps around again to 0.</li>
<li>The GREEN channel follows the same process, but first the key is bit shifted to the LEFT by 1 bit</li>
<li>The BLUE channel follows the same process, but first the key is bit shifted to the RIGHT by 1 bit</li>
</ol></li>
</ol>
<p>
For example, consider a single pixel value <code>(123, 12, 34, 132)</code>.
</p>
<p>
The encoded value would be:
</p>
<pre class="example">
( (123 + 100 * 132) % 256,
( 12 + 100 * 132 << 1) % 256,
( 34 + 100 * 132 >> 1) % 256,
132 )
</pre>
<p>
All you need to do to decode the image is to reverse these steps. What is the gift you need to send?
</p>
</div>
</div>
<div id="outline-container-org148a76a" class="outline-2">
<h2 id="org148a76a"><span class="section-number-2">4.</span> Problem: Part 2</h2>
<div class="outline-text-2" id="text-4">
<p>
Oh no! A crucial piece of information is missing! Being a highly suspicious and unstable conspiracy theorist, believing that all communication channels are being observed by Grinch (who is intent on ruining Christmas), he encrypted some information before sending his letter to Santa.
</p>
<p>
You’ll have to apply what you’ve learned already to decode it. What is the missing information?
</p>
</div>
</div>
</div>
<div id="postamble" class="status">
<p class="author">Author: Neil Forrest</p>
<p class="date">Created: 2022-12-22 Thu 14:10</p>
</div>
</body>
</html>