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<!DOCTYPE html>
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<title>2021/day14.nim</title>
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<span><a href="..">🏡</a></span>
<span><code>2021/day14.nim</code></span>
<span><a href="https://github.com/pietroppeter/adventofnim"><svg aria-hidden="true" width="1.2em" height="1.2em" style="vertical-align: middle; fill: #fff" preserveAspectRatio="xMidYMid meet" viewBox="0 0 16 16"><path fill-rule="evenodd" d="M8 0C3.58 0 0 3.58 0 8c0 3.54 2.29 6.53 5.47 7.59.4.07.55-.17.55-.38 0-.19-.01-.82-.01-1.49-2.01.37-2.53-.49-2.69-.94-.09-.23-.48-.94-.82-1.13-.28-.15-.68-.52-.01-.53.63-.01 1.08.58 1.23.82.72 1.21 1.87.87 2.33.66.07-.52.28-.87.51-1.07-1.78-.2-3.64-.89-3.64-3.95 0-.87.31-1.59.82-2.15-.08-.2-.36-1.02.08-2.12 0 0 .67-.21 2.2.82.64-.18 1.32-.27 2-.27.68 0 1.36.09 2 .27 1.53-1.04 2.2-.82 2.2-.82.44 1.1.16 1.92.08 2.12.51.56.82 1.27.82 2.15 0 3.07-1.87 3.75-3.65 3.95.29.25.54.73.54 1.48 0 1.07-.01 1.93-.01 2.2 0 .21.15.46.55.38A8.013 8.013 0 0016 8c0-4.42-3.58-8-8-8z"></path></svg></a></span>
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<h2>Day 14: <a href="https://adventofcode.com/2021/day/14">Extended Polymerization</a></h2>
<p>Today is a chemistry day!</p>
<h3>Part 1</h3>
<p>Parsing is straightforward</p>
<pre><code class="nim hljs"><span class="hljs-keyword">type</span> <span class="hljs-type">Rules</span> = <span class="hljs-type">Table</span>[<span class="hljs-built_in">string</span>, <span class="hljs-built_in">char</span>]
<span class="hljs-keyword">func</span> parse(text: <span class="hljs-built_in">string</span>): <span class="hljs-type">Rules</span> =
<span class="hljs-literal">result</span> = initTable[<span class="hljs-built_in">string</span>, <span class="hljs-built_in">char</span>]()
<span class="hljs-keyword">for</span> line <span class="hljs-keyword">in</span> text.splitLines:
<span class="hljs-literal">result</span>[line[<span class="hljs-number">0</span> .. <span class="hljs-number">1</span>]] = line.strip[^<span class="hljs-number">1</span>]
<span class="hljs-keyword">let</span>
testTemplate = <span class="hljs-string">"NNCB"</span>
puzzleTemplate = <span class="hljs-string">"VNVVKSNNFPBBBVSCVBBC"</span>
testRules = parse <span class="hljs-string">"""
CH -> B
HH -> N
CB -> H
NH -> C
HB -> C
HC -> B
HN -> C
NN -> C
BH -> H
NC -> B
NB -> B
BN -> B
BB -> N
BC -> B
CC -> N
CN -> C"""</span>
puzzleRules = parse readFile(<span class="hljs-string">"2021/input14.txt"</span>)
dump testRules[<span class="hljs-string">"BB"</span>]
dump testRules.len
dump puzzleRules[<span class="hljs-string">"BB"</span>]
dump puzzleRules.len</code></pre>
<pre><samp>testRules["BB"] = N
testRules.len = 16
puzzleRules["BB"] = H
puzzleRules.len = 100
</samp></pre>
<p>Let's write the evolution function:</p>
<pre><code class="nim hljs"><span class="hljs-keyword">func</span> tick(rules: <span class="hljs-type">Rules</span>, polymer: <span class="hljs-built_in">string</span>): <span class="hljs-built_in">string</span> =
<span class="hljs-literal">result</span>.add polymer[<span class="hljs-number">0</span>]
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> ..< polymer.<span class="hljs-keyword">high</span>: <span class="hljs-comment"># until 1 less than highest index</span>
<span class="hljs-keyword">let</span> pair = polymer[i .. (i+<span class="hljs-number">1</span>)]
<span class="hljs-keyword">if</span> pair <span class="hljs-keyword">in</span> rules:
<span class="hljs-literal">result</span>.add rules[pair]
<span class="hljs-literal">result</span>.add polymer[i+<span class="hljs-number">1</span>]
<span class="hljs-keyword">func</span> tickN(rules: <span class="hljs-type">Rules</span>, polymer: <span class="hljs-built_in">string</span>, n=<span class="hljs-number">10</span>): <span class="hljs-built_in">string</span> =
<span class="hljs-literal">result</span> = polymer
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">1</span> .. n:
<span class="hljs-literal">result</span> = rules.tick <span class="hljs-literal">result</span>
debugEcho i, <span class="hljs-string">": "</span>, <span class="hljs-literal">result</span>.len
dump testRules.tick testTemplate
dump testRules.tickN(testTemplate, n=<span class="hljs-number">2</span>)
dump testRules.tickN(testTemplate, n=<span class="hljs-number">3</span>)
dump testRules.tickN(testTemplate, n=<span class="hljs-number">4</span>)</code></pre>
<pre><samp>testRules.tick testTemplate = NCNBCHB
1: 7
2: 13
testRules.tickN(testTemplate, n = 2) = NBCCNBBBCBHCB
1: 7
2: 13
3: 25
testRules.tickN(testTemplate, n = 3) = NBBBCNCCNBBNBNBBCHBHHBCHB
1: 7
2: 13
3: 25
4: 49
testRules.tickN(testTemplate, n = 4) = NBBNBNBBCCNBCNCCNBBNBBNBBBNBBNBBCBHCBHHNHCBBCBHCB
</samp></pre>
<p>and let's solve part 1</p>
<pre><code class="nim hljs"><span class="hljs-keyword">func</span> part1(rules: <span class="hljs-type">Rules</span>, polymer: <span class="hljs-built_in">string</span>, n=<span class="hljs-number">10</span>): <span class="hljs-built_in">int</span> =
<span class="hljs-keyword">let</span> polymer = rules.tickN(polymer, n)
<span class="hljs-keyword">var</span> elementCountTable = polymer.toCountTable
elementCountTable.sort() <span class="hljs-comment"># default order is descending</span>
<span class="hljs-keyword">let</span>
keys = toSeq(elementCountTable.keys)
counts = toSeq(elementCountTable.values)
debugEcho <span class="hljs-string">"max: "</span>, keys[<span class="hljs-number">0</span>], <span class="hljs-string">" -> "</span>, counts[<span class="hljs-number">0</span>]
debugEcho <span class="hljs-string">"min: "</span>, keys[^<span class="hljs-number">1</span>], <span class="hljs-string">" -> "</span>, counts[^<span class="hljs-number">1</span>]
counts[<span class="hljs-number">0</span>] - counts[^<span class="hljs-number">1</span>]
dump part1(testRules, testTemplate)
dump part1(puzzleRules, puzzleTemplate)</code></pre>
<pre><samp>1: 7
2: 13
3: 25
4: 49
5: 97
6: 193
7: 385
8: 769
9: 1537
10: 3073
max: B -> 1749
min: H -> 161
part1(testRules, testTemplate) = 1588
1: 39
2: 77
3: 153
4: 305
5: 609
6: 1217
7: 2433
8: 4865
9: 9729
10: 19457
max: H -> 3618
min: C -> 997
part1(puzzleRules, puzzleTemplate) = 2621
</samp></pre>
<blockquote>
<p>That's the right answer! You are <em class="star">one gold star</em> closer to saving your vacation.</p>
</blockquote>
<p>all good except I did not read well and first implemented a function to count pairs
and not use the builtin for counting single elements (hence the <code>debugEchos</code>)</p>
<h2>Part 2</h2>
<p>ok, here clearly the brute force approach we used is not supposed to work and I am pretty sure
I am going to need the <code>countPairs</code> I just deleted...</p>
<pre><code class="nim hljs"><span class="hljs-comment"># had to try anyway, but after a few seconds I stopped</span>
<span class="hljs-comment">#dump part1(testRules, testTemplate, n=40)</span>
<span class="hljs-comment">#dump part1(puzzleRules, puzzleTemplate, n=40)</span>
<span class="hljs-keyword">discard</span> <span class="hljs-comment"># cannot have a code block with only comments!</span></code></pre>
<pre><code class="nim hljs"><span class="hljs-keyword">type</span> <span class="hljs-type">CountPairs</span> = <span class="hljs-type">CountTable</span>[<span class="hljs-built_in">string</span>]
<span class="hljs-keyword">func</span> getCountPairs(polymer: <span class="hljs-built_in">string</span>): <span class="hljs-type">CountPairs</span> =
<span class="hljs-literal">result</span> = initCountTable[<span class="hljs-built_in">string</span>]()
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> ..< polymer.<span class="hljs-keyword">high</span>:
<span class="hljs-keyword">let</span> pair = polymer[i .. (i+<span class="hljs-number">1</span>)]
<span class="hljs-literal">result</span>.inc pair
<span class="hljs-keyword">func</span> tick(rules: <span class="hljs-type">Rules</span>, countPairs: <span class="hljs-type">CountPairs</span>): <span class="hljs-type">CountPairs</span> =
<span class="hljs-literal">result</span> = initCountTable[<span class="hljs-built_in">string</span>]()
<span class="hljs-keyword">for</span> pair <span class="hljs-keyword">in</span> countPairs.keys:
<span class="hljs-keyword">if</span> pair <span class="hljs-keyword">in</span> rules:
<span class="hljs-keyword">let</span>
count = countPairs[pair]
newPairLeft = pair[<span class="hljs-number">0</span>] & rules[pair]
newPairRight = rules[pair] & pair[<span class="hljs-number">1</span>]
<span class="hljs-literal">result</span>.inc(newPairLeft, count)
<span class="hljs-literal">result</span>.inc(newPairRight, count)
<span class="hljs-keyword">func</span> tickN(rules: <span class="hljs-type">Rules</span>, countPairs: <span class="hljs-type">CountPairs</span>, n=<span class="hljs-number">40</span>): <span class="hljs-type">CountPairs</span> =
<span class="hljs-literal">result</span> = countPairs
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">1</span> .. n:
<span class="hljs-literal">result</span> = rules.tick <span class="hljs-literal">result</span>
debugEcho i, <span class="hljs-string">": "</span>, <span class="hljs-literal">result</span>.len <span class="hljs-comment"># how many pairs</span>
<span class="hljs-keyword">func</span> part2(rules: <span class="hljs-type">Rules</span>, polymer: <span class="hljs-built_in">string</span>, n=<span class="hljs-number">40</span>): <span class="hljs-built_in">int</span> =
<span class="hljs-keyword">var</span> countPairs = polymer.getCountPairs
countPairs = rules.tickN(countPairs, n)
<span class="hljs-keyword">var</span> elementCountTable = initCountTable[<span class="hljs-built_in">char</span>]()
<span class="hljs-keyword">for</span> pair, count <span class="hljs-keyword">in</span> countPairs:
elementCountTable.inc(pair[<span class="hljs-number">1</span>], val=count)
elementCountTable.inc(polymer[<span class="hljs-number">0</span>]) <span class="hljs-comment"># need to count again first element</span>
elementCountTable.sort() <span class="hljs-comment"># default order is descending</span>
<span class="hljs-keyword">let</span>
keys = toSeq(elementCountTable.keys)
counts = toSeq(elementCountTable.values)
debugEcho <span class="hljs-string">"max: "</span>, keys[<span class="hljs-number">0</span>], <span class="hljs-string">" -> "</span>, counts[<span class="hljs-number">0</span>]
debugEcho <span class="hljs-string">"min: "</span>, keys[^<span class="hljs-number">1</span>], <span class="hljs-string">" -> "</span>, counts[^<span class="hljs-number">1</span>]
counts[<span class="hljs-number">0</span>] - counts[^<span class="hljs-number">1</span>]
dump part2(testRules, testTemplate, n=<span class="hljs-number">10</span>)
dump part2(puzzleRules, puzzleTemplate, n=<span class="hljs-number">10</span>)</code></pre>
<pre><samp>1: 6
2: 8
3: 11
4: 13
5: 14
6: 15
7: 15
8: 15
9: 15
10: 15
max: B -> 1749
min: H -> 161
part2(testRules, testTemplate, n = 10) = 1588
1: 30
2: 47
3: 62
4: 73
5: 77
6: 78
7: 78
8: 78
9: 78
10: 78
max: H -> 3618
min: C -> 997
part2(puzzleRules, puzzleTemplate, n = 10) = 2621
</samp></pre>
<p>ok, checks out with part 1</p>
<pre><code class="nim hljs">dump part2(testRules, testTemplate, n=<span class="hljs-number">40</span>)
dump part2(puzzleRules, puzzleTemplate, n=<span class="hljs-number">40</span>)</code></pre>
<pre><samp>1: 6
2: 8
3: 11
4: 13
5: 14
6: 15
7: 15
8: 15
9: 15
10: 15
11: 15
12: 15
13: 15
14: 15
15: 15
16: 15
17: 15
18: 15
19: 15
20: 15
21: 15
22: 15
23: 15
24: 15
25: 15
26: 15
27: 15
28: 15
29: 15
30: 15
31: 15
32: 15
33: 15
34: 15
35: 15
36: 15
37: 15
38: 15
39: 15
40: 15
max: B -> 2192039569602
min: H -> 3849876073
part2(testRules, testTemplate, n = 40) = 2188189693529
1: 30
2: 47
3: 62
4: 73
5: 77
6: 78
7: 78
8: 78
9: 78
10: 78
11: 78
12: 78
13: 78
14: 78
15: 78
16: 78
17: 78
18: 78
19: 78
20: 78
21: 78
22: 78
23: 78
24: 78
25: 78
26: 78
27: 78
28: 78
29: 78
30: 78
31: 78
32: 78
33: 78
34: 78
35: 78
36: 78
37: 78
38: 78
39: 78
40: 78
max: H -> 3918098460190
min: C -> 1074264218824
part2(puzzleRules, puzzleTemplate, n = 40) = 2843834241366
</samp></pre>
<blockquote>
<p>That's the right answer! You are <em class="star">one gold star</em> closer to saving your vacation.</p>
</blockquote>
<p>surprised I got the second part at first try (had to think a bit to get it correct)!</p>
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<pre><code class="nim hljs"><span class="hljs-keyword">import</span> animu, nimib
nbInit(theme=useAdventOfNim)
nbText: <span class="hljs-string">"""## Day 14: [Extended Polymerization](https://adventofcode.com/2021/day/14)
Today is a chemistry day!
### Part 1
Parsing is straightforward
"""</span>
nbCode:
<span class="hljs-keyword">type</span> <span class="hljs-type">Rules</span> = <span class="hljs-type">Table</span>[<span class="hljs-built_in">string</span>, <span class="hljs-built_in">char</span>]
<span class="hljs-keyword">func</span> parse(text: <span class="hljs-built_in">string</span>): <span class="hljs-type">Rules</span> =
<span class="hljs-literal">result</span> = initTable[<span class="hljs-built_in">string</span>, <span class="hljs-built_in">char</span>]()
<span class="hljs-keyword">for</span> line <span class="hljs-keyword">in</span> text.splitLines:
<span class="hljs-literal">result</span>[line[<span class="hljs-number">0</span> .. <span class="hljs-number">1</span>]] = line.strip[^<span class="hljs-number">1</span>]
<span class="hljs-keyword">let</span>
testTemplate = <span class="hljs-string">"NNCB"</span>
puzzleTemplate = <span class="hljs-string">"VNVVKSNNFPBBBVSCVBBC"</span>
testRules = parse <span class="hljs-string">"""
CH -> B
HH -> N
CB -> H
NH -> C
HB -> C
HC -> B
HN -> C
NN -> C
BH -> H
NC -> B
NB -> B
BN -> B
BB -> N
BC -> B
CC -> N
CN -> C"""</span>
puzzleRules = parse readFile(<span class="hljs-string">"2021/input14.txt"</span>)
dump testRules[<span class="hljs-string">"BB"</span>]
dump testRules.len
dump puzzleRules[<span class="hljs-string">"BB"</span>]
dump puzzleRules.len
nbText: <span class="hljs-string">"Let's write the evolution function:"</span>
nbCode:
<span class="hljs-keyword">func</span> tick(rules: <span class="hljs-type">Rules</span>, polymer: <span class="hljs-built_in">string</span>): <span class="hljs-built_in">string</span> =
<span class="hljs-literal">result</span>.add polymer[<span class="hljs-number">0</span>]
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> ..< polymer.<span class="hljs-keyword">high</span>: <span class="hljs-comment"># until 1 less than highest index</span>
<span class="hljs-keyword">let</span> pair = polymer[i .. (i+<span class="hljs-number">1</span>)]
<span class="hljs-keyword">if</span> pair <span class="hljs-keyword">in</span> rules:
<span class="hljs-literal">result</span>.add rules[pair]
<span class="hljs-literal">result</span>.add polymer[i+<span class="hljs-number">1</span>]
<span class="hljs-keyword">func</span> tickN(rules: <span class="hljs-type">Rules</span>, polymer: <span class="hljs-built_in">string</span>, n=<span class="hljs-number">10</span>): <span class="hljs-built_in">string</span> =
<span class="hljs-literal">result</span> = polymer
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">1</span> .. n:
<span class="hljs-literal">result</span> = rules.tick <span class="hljs-literal">result</span>
debugEcho i, <span class="hljs-string">": "</span>, <span class="hljs-literal">result</span>.len
dump testRules.tick testTemplate
dump testRules.tickN(testTemplate, n=<span class="hljs-number">2</span>)
dump testRules.tickN(testTemplate, n=<span class="hljs-number">3</span>)
dump testRules.tickN(testTemplate, n=<span class="hljs-number">4</span>)
nbText: <span class="hljs-string">"and let's solve part 1"</span>
nbCode:
<span class="hljs-keyword">func</span> part1(rules: <span class="hljs-type">Rules</span>, polymer: <span class="hljs-built_in">string</span>, n=<span class="hljs-number">10</span>): <span class="hljs-built_in">int</span> =
<span class="hljs-keyword">let</span> polymer = rules.tickN(polymer, n)
<span class="hljs-keyword">var</span> elementCountTable = polymer.toCountTable
elementCountTable.sort() <span class="hljs-comment"># default order is descending</span>
<span class="hljs-keyword">let</span>
keys = toSeq(elementCountTable.keys)
counts = toSeq(elementCountTable.values)
debugEcho <span class="hljs-string">"max: "</span>, keys[<span class="hljs-number">0</span>], <span class="hljs-string">" -> "</span>, counts[<span class="hljs-number">0</span>]
debugEcho <span class="hljs-string">"min: "</span>, keys[^<span class="hljs-number">1</span>], <span class="hljs-string">" -> "</span>, counts[^<span class="hljs-number">1</span>]
counts[<span class="hljs-number">0</span>] - counts[^<span class="hljs-number">1</span>]
dump part1(testRules, testTemplate)
dump part1(puzzleRules, puzzleTemplate)
gotTheStar
nbText: <span class="hljs-string">"""all good except I did not read well and first implemented a function to count pairs
and not use the builtin for counting single elements (hence the `debugEchos`)
## Part 2
ok, here clearly the brute force approach we used is not supposed to work and I am pretty sure
I am going to need the `countPairs` I just deleted...
"""</span>
nbCode:
<span class="hljs-comment"># had to try anyway, but after a few seconds I stopped</span>
<span class="hljs-comment">#dump part1(testRules, testTemplate, n=40)</span>
<span class="hljs-comment">#dump part1(puzzleRules, puzzleTemplate, n=40)</span>
<span class="hljs-keyword">discard</span> <span class="hljs-comment"># cannot have a code block with only comments!</span>
nbCode:
<span class="hljs-keyword">type</span> <span class="hljs-type">CountPairs</span> = <span class="hljs-type">CountTable</span>[<span class="hljs-built_in">string</span>]
<span class="hljs-keyword">func</span> getCountPairs(polymer: <span class="hljs-built_in">string</span>): <span class="hljs-type">CountPairs</span> =
<span class="hljs-literal">result</span> = initCountTable[<span class="hljs-built_in">string</span>]()
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> ..< polymer.<span class="hljs-keyword">high</span>:
<span class="hljs-keyword">let</span> pair = polymer[i .. (i+<span class="hljs-number">1</span>)]
<span class="hljs-literal">result</span>.inc pair
<span class="hljs-keyword">func</span> tick(rules: <span class="hljs-type">Rules</span>, countPairs: <span class="hljs-type">CountPairs</span>): <span class="hljs-type">CountPairs</span> =
<span class="hljs-literal">result</span> = initCountTable[<span class="hljs-built_in">string</span>]()
<span class="hljs-keyword">for</span> pair <span class="hljs-keyword">in</span> countPairs.keys:
<span class="hljs-keyword">if</span> pair <span class="hljs-keyword">in</span> rules:
<span class="hljs-keyword">let</span>
count = countPairs[pair]
newPairLeft = pair[<span class="hljs-number">0</span>] & rules[pair]
newPairRight = rules[pair] & pair[<span class="hljs-number">1</span>]
<span class="hljs-literal">result</span>.inc(newPairLeft, count)
<span class="hljs-literal">result</span>.inc(newPairRight, count)
<span class="hljs-keyword">func</span> tickN(rules: <span class="hljs-type">Rules</span>, countPairs: <span class="hljs-type">CountPairs</span>, n=<span class="hljs-number">40</span>): <span class="hljs-type">CountPairs</span> =
<span class="hljs-literal">result</span> = countPairs
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">1</span> .. n:
<span class="hljs-literal">result</span> = rules.tick <span class="hljs-literal">result</span>
debugEcho i, <span class="hljs-string">": "</span>, <span class="hljs-literal">result</span>.len <span class="hljs-comment"># how many pairs</span>
<span class="hljs-keyword">func</span> part2(rules: <span class="hljs-type">Rules</span>, polymer: <span class="hljs-built_in">string</span>, n=<span class="hljs-number">40</span>): <span class="hljs-built_in">int</span> =
<span class="hljs-keyword">var</span> countPairs = polymer.getCountPairs
countPairs = rules.tickN(countPairs, n)
<span class="hljs-keyword">var</span> elementCountTable = initCountTable[<span class="hljs-built_in">char</span>]()
<span class="hljs-keyword">for</span> pair, count <span class="hljs-keyword">in</span> countPairs:
elementCountTable.inc(pair[<span class="hljs-number">1</span>], val=count)
elementCountTable.inc(polymer[<span class="hljs-number">0</span>]) <span class="hljs-comment"># need to count again first element</span>
elementCountTable.sort() <span class="hljs-comment"># default order is descending</span>
<span class="hljs-keyword">let</span>
keys = toSeq(elementCountTable.keys)
counts = toSeq(elementCountTable.values)
debugEcho <span class="hljs-string">"max: "</span>, keys[<span class="hljs-number">0</span>], <span class="hljs-string">" -> "</span>, counts[<span class="hljs-number">0</span>]
debugEcho <span class="hljs-string">"min: "</span>, keys[^<span class="hljs-number">1</span>], <span class="hljs-string">" -> "</span>, counts[^<span class="hljs-number">1</span>]
counts[<span class="hljs-number">0</span>] - counts[^<span class="hljs-number">1</span>]
dump part2(testRules, testTemplate, n=<span class="hljs-number">10</span>)
dump part2(puzzleRules, puzzleTemplate, n=<span class="hljs-number">10</span>)
nbText: <span class="hljs-string">"ok, checks out with part 1"</span>
nbCode:
dump part2(testRules, testTemplate, n=<span class="hljs-number">40</span>)
dump part2(puzzleRules, puzzleTemplate, n=<span class="hljs-number">40</span>)
gotTheStar
nbText: <span class="hljs-string">"surprised I got the second part at first try (had to think a bit to get it correct)!"</span>
nbSave</code></pre>
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