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2021</title>
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16 Oh, hello! Funny seeing you here.
18 I appreciate your enthusiasm, but you aren't going to find much down here.
19 There certainly aren't clues to any of the puzzles. The best surprises don't
20 even appear in the source until you unlock them for real.
22 Please be careful with automated requests; I'm not a massive company, and I can
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25 If you're curious about how Advent of Code works, it's running on some custom
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27 built the whole thing myself, including the design, animations, prose, and all
30 The puzzles are most of the work; preparing a new calendar and a new set of
31 puzzles each year takes all of my free time for 4-5 months. A lot of effort
32 went into building this thing - I hope you're enjoying playing it as much as I
33 enjoyed making it for you!
35 If you'd like to hang out, I'm @ericwastl on Twitter.
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98 <article class=
"day-desc"><h2>--- Day
14: Extended Polymerization ---
</h2><p>The incredible pressures at this depth are starting to put a strain on your submarine. The submarine has
<a href=
"https://en.wikipedia.org/wiki/Polymerization" target=
"_blank">polymerization
</a> equipment that would produce suitable materials to reinforce the submarine, and the nearby volcanically-active caves should even have the necessary input elements in sufficient quantities.
</p>
99 <p>The submarine manual contains
<span title=
"HO

HO -> OH">instructions
</span> for finding the optimal polymer formula; specifically, it offers a
<em>polymer template
</em> and a list of
<em>pair insertion
</em> rules (your puzzle input). You just need to work out what polymer would result after repeating the pair insertion process a few times.
</p>
120 <p>The first line is the
<em>polymer template
</em> - this is the starting point of the process.
</p>
121 <p>The following section defines the
<em>pair insertion
</em> rules. A rule like
<code>AB -
> C
</code> means that when elements
<code>A
</code> and
<code>B
</code> are immediately adjacent, element
<code>C
</code> should be inserted between them. These insertions all happen simultaneously.
</p>
122 <p>So, starting with the polymer template
<code>NNCB
</code>, the first step simultaneously considers all three pairs:
</p>
124 <li>The first pair (
<code>NN
</code>) matches the rule
<code>NN -
> C
</code>, so element
<code><em>C
</em></code> is inserted between the first
<code>N
</code> and the second
<code>N
</code>.
</li>
125 <li>The second pair (
<code>NC
</code>) matches the rule
<code>NC -
> B
</code>, so element
<code><em>B
</em></code> is inserted between the
<code>N
</code> and the
<code>C
</code>.
</li>
126 <li>The third pair (
<code>CB
</code>) matches the rule
<code>CB -
> H
</code>, so element
<code><em>H
</em></code> is inserted between the
<code>C
</code> and the
<code>B
</code>.
</li>
128 <p>Note that these pairs overlap: the second element of one pair is the first element of the next pair. Also, because all pairs are considered simultaneously, inserted elements are not considered to be part of a pair until the next step.
</p>
129 <p>After the first step of this process, the polymer becomes
<code>N
<em>C
</em>N
<em>B
</em>C
<em>H
</em>B
</code>.
</p>
130 <p>Here are the results of a few steps using the above rules:
</p>
131 <pre><code>Template: NNCB
132 After step
1: NCNBCHB
133 After step
2: NBCCNBBBCBHCB
134 After step
3: NBBBCNCCNBBNBNBBCHBHHBCHB
135 After step
4: NBBNBNBBCCNBCNCCNBBNBBNBBBNBBNBBCBHCBHHNHCBBCBHCB
137 <p>This polymer grows quickly. After step
5, it has length
97; After step
10, it has length
3073. After step
10,
<code>B
</code> occurs
1749 times,
<code>C
</code> occurs
298 times,
<code>H
</code> occurs
161 times, and
<code>N
</code> occurs
865 times; taking the quantity of the most common element (
<code>B
</code>,
1749) and subtracting the quantity of the least common element (
<code>H
</code>,
161) produces
<code>1749 -
161 =
<em>1588</em></code>.
</p>
138 <p>Apply
10 steps of pair insertion to the polymer template and find the most and least common elements in the result.
<em>What do you get if you take the quantity of the most common element and subtract the quantity of the least common element?
</em></p>
140 <p>Your puzzle answer was
<code>2712</code>.
</p><article class=
"day-desc"><h2 id=
"part2">--- Part Two ---
</h2><p>The resulting polymer isn't nearly strong enough to reinforce the submarine. You'll need to run more steps of the pair insertion process; a total of
<em>40 steps
</em> should do it.
</p>
141 <p>In the above example, the most common element is
<code>B
</code> (occurring
<code>2192039569602</code> times) and the least common element is
<code>H
</code> (occurring
<code>3849876073</code> times); subtracting these produces
<code><em>2188189693529</em></code>.
</p>
142 <p>Apply
<em>40</em> steps of pair insertion to the polymer template and find the most and least common elements in the result.
<em>What do you get if you take the quantity of the most common element and subtract the quantity of the least common element?
</em></p>
144 <p>Your puzzle answer was
<code>8336623059567</code>.
</p><p class=
"day-success">Both parts of this puzzle are complete! They provide two gold stars: **
</p>
145 <p>At this point, you should
<a href=
"/2021">return to your Advent calendar
</a> and try another puzzle.
</p>
146 <p>If you still want to see it, you can
<a href=
"14/input" target=
"_blank">get your puzzle input
</a>.
</p>
147 <p>You can also
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"share">[Share
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