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<!DOCTYPE html>
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<title>2020\day09.nim</title>
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<span><a href="..">🏡</a></span>
<span><code>2020\day09.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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<h1>2020, Day 9: Encoding Error</h1>
<p>This turned out be to nice and easy but it does give satisfaction.</p>
<p>The strategy for first part is to use at the same time a <code>deque</code> and a <code>intset</code>
(<em>hey, I did not know there is a new <a href="https://nim-lang.github.io/Nim/packedsets.html"><code>packedset</code></a> that will generalize and replace
<code>intset</code></em>).</p>
<p>The second part was rather straightforward with two nested for loops.</p>
<p>I would say anyway the main technique here is a wise use of <code>break</code> statement,
especially using named blocks.</p>
<p>But first things first, parsing the input this time is a simple one-liner:</p>
<pre><code class="nim hljs"><span class="hljs-keyword">proc</span> parse(text: <span class="hljs-built_in">string</span>): <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>] =
text.splitLines.map(parseInt)
<span class="hljs-keyword">let</span>
input = parse <span class="hljs-string">"2020/input09.txt"</span>.readFile
example = parse <span class="hljs-string">"""35
20
15
25
47
40
62
55
65
95
102
117
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182
127
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299
277
309
576"""</span>
<span class="hljs-keyword">echo</span> input.len
<span class="hljs-keyword">echo</span> example.len</code></pre>
<pre><samp>1000
20</samp></pre>
<p>and I can pack the solution in a single proc:</p>
<pre><code class="nim hljs"><span class="hljs-keyword">proc</span> solve(s: <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>]; l: <span class="hljs-built_in">int</span>): (<span class="hljs-built_in">int</span>, <span class="hljs-built_in">int</span>) =
<span class="hljs-keyword">var</span>
d = initDeque[<span class="hljs-built_in">int</span>]()
p = initIntSet() <span class="hljs-comment">## p stands for packedsets, I tried to use it but I do not have it yet</span>
<span class="hljs-comment">## </span>
<span class="hljs-comment">## d and p are synchronized to contain same stuff</span>
n: <span class="hljs-built_in">int</span>
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> ..< l:
d.addLast(s[i])
p.incl s[i]
<span class="hljs-keyword">block</span> findInvalid:
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> l ..< s.len:
n = s[i]
<span class="hljs-keyword">block</span> findPair:
<span class="hljs-keyword">for</span> m <span class="hljs-keyword">in</span> d:
<span class="hljs-keyword">if</span> n != m <span class="hljs-keyword">and</span> n - m <span class="hljs-keyword">in</span> p:
<span class="hljs-keyword">break</span> findPair
<span class="hljs-comment">## if I get here it means I have not found a sum!</span>
<span class="hljs-keyword">break</span> findInvalid <span class="hljs-comment">## n is answer for part1</span>
p.incl n
p.excl d.popFirst
d.addLast n
<span class="hljs-comment">## part 2</span>
<span class="hljs-keyword">var</span>
nMin, nMax: <span class="hljs-built_in">int</span>
cumSum = s[<span class="hljs-number">0</span>]
<span class="hljs-keyword">block</span> findSum:
<span class="hljs-keyword">for</span> k <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> ..< s.len:
cumSum = <span class="hljs-number">0</span>
nMin = <span class="hljs-built_in">int</span>.<span class="hljs-keyword">high</span>
nMax = <span class="hljs-number">0</span>
<span class="hljs-keyword">for</span> l <span class="hljs-keyword">in</span> k ..< s.len:
cumSum += s[l]
<span class="hljs-keyword">if</span> s[l] < nMin:
nMin = s[l]
<span class="hljs-keyword">if</span> s[l] > nMax:
nMax = s[l]
<span class="hljs-keyword">if</span> cumSum == n:
<span class="hljs-keyword">break</span> findSum
<span class="hljs-keyword">if</span> cumSum > n:
<span class="hljs-keyword">break</span>
<span class="hljs-keyword">return</span> (n, nMin + nMax)
<span class="hljs-keyword">echo</span> solve(example, <span class="hljs-number">5</span>) <span class="hljs-comment">## 127, 62</span>
<span class="hljs-keyword">echo</span> solve(input, <span class="hljs-number">25</span>) <span class="hljs-comment">## 133015568, 16107959</span></code></pre>
<pre><samp>(127, 62)
(133015568, 16107959)</samp></pre>
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<pre><code class="nim hljs"><span class="hljs-keyword">import</span> nimib
<span class="hljs-keyword">import</span> deques, sequtils, parseutils, strutils, intsets
nbInit
nbText: <span class="hljs-string">"""# 2020, Day 9: Encoding Error
This turned out be to nice and easy but it does give satisfaction.
The strategy for first part is to use at the same time a `deque` and a `intset`
(*hey, I did not know there is a new [`packedset`](https://nim-lang.github.io/Nim/packedsets.html) that will generalize and replace
`intset`*).
The second part was rather straightforward with two nested for loops.
I would say anyway the main technique here is a wise use of `break` statement,
especially using named blocks.
But first things first, parsing the input this time is a simple one-liner:
"""</span>
nbCode:
<span class="hljs-keyword">proc</span> parse(text: <span class="hljs-built_in">string</span>): <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>] = text.splitLines.map(parseInt)
<span class="hljs-keyword">let</span>
input = parse <span class="hljs-string">"2020/input09.txt"</span>.readFile
example = parse <span class="hljs-string">"""35
20
15
25
47
40
62
55
65
95
102
117
150
182
127
219
299
277
309
576"""</span>
<span class="hljs-keyword">echo</span> input.len
<span class="hljs-keyword">echo</span> example.len
<span class="hljs-comment"># as usual when converting to nimib I fuck up the example...</span>
nbText: <span class="hljs-string">"and I can pack the solution in a single proc:"</span>
nbCode:
<span class="hljs-keyword">proc</span> solve(s: <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>], l: <span class="hljs-built_in">int</span>): (<span class="hljs-built_in">int</span>, <span class="hljs-built_in">int</span>) =
<span class="hljs-keyword">var</span>
d = initDeque[<span class="hljs-built_in">int</span>]()
p = initIntSet() <span class="hljs-comment">## p stands for packedsets, I tried to use it but I do not have it yet</span>
<span class="hljs-comment">## d and p are synchronized to contain same stuff</span>
n: <span class="hljs-built_in">int</span>
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> ..< l:
d.addLast(s[i])
p.incl s[i]
<span class="hljs-keyword">block</span> findInvalid:
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> l ..< s.len:
n = s[i]
<span class="hljs-keyword">block</span> findPair:
<span class="hljs-keyword">for</span> m <span class="hljs-keyword">in</span> d:
<span class="hljs-keyword">if</span> n != m <span class="hljs-keyword">and</span> n - m <span class="hljs-keyword">in</span> p: <span class="hljs-keyword">break</span> findPair
<span class="hljs-comment">## if I get here it means I have not found a sum!</span>
<span class="hljs-keyword">break</span> findInvalid <span class="hljs-comment">## n is answer for part1</span>
p.incl n
p.excl d.popFirst
d.addLast n
<span class="hljs-comment">## part 2</span>
<span class="hljs-keyword">var</span>
nMin, nMax: <span class="hljs-built_in">int</span>
cumSum = s[<span class="hljs-number">0</span>]
<span class="hljs-keyword">block</span> findSum:
<span class="hljs-keyword">for</span> k <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> ..< s.len:
cumSum = <span class="hljs-number">0</span>
nMin = <span class="hljs-built_in">int</span>.<span class="hljs-keyword">high</span>
nMax = <span class="hljs-number">0</span>
<span class="hljs-keyword">for</span> l <span class="hljs-keyword">in</span> k ..< s.len:
cumSum += s[l]
<span class="hljs-keyword">if</span> s[l] < nMin:
nMin = s[l]
<span class="hljs-keyword">if</span> s[l] > nMax:
nMax = s[l]
<span class="hljs-keyword">if</span> cumSum == n:
<span class="hljs-keyword">break</span> findSum
<span class="hljs-keyword">if</span> cumSum > n:
<span class="hljs-keyword">break</span>
<span class="hljs-keyword">return</span> (n, nMin + nMax)
<span class="hljs-keyword">echo</span> solve(example, <span class="hljs-number">5</span>) <span class="hljs-comment">## 127, 62</span>
<span class="hljs-keyword">echo</span> solve(input, <span class="hljs-number">25</span>) <span class="hljs-comment">## 133015568, 16107959</span>
nbSave</code></pre>
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