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<!DOCTYPE html>
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<head>
<title>2020\day14.nim</title>
<link rel="icon" href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 100 100%22><text y=%22.9em%22 font-size=%2280%22>🐳</text></svg>">
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<div class="nb-box">
<span><a href="..">🏡</a></span>
<span><code>2020\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>2020, Day 14: Docking Data 🚢 💽</h2>
<p>Today was an opportunity to learn more about <a href="https://nim-lang.org/docs/bitops.html">bitops</a>.</p>
<pre><code class="nim hljs"><span class="hljs-keyword">import</span>
bitops, tables, algorithm, math, strscans, strutils</code></pre>
<p>For part 1 I first make sure I can parse the mask. <code>floating</code> field is a result of refactoring for part 2.</p>
<pre><code class="nim hljs"><span class="hljs-keyword">type</span>
<span class="hljs-type">Mask</span> = <span class="hljs-keyword">object</span>
ones: <span class="hljs-built_in">int</span>
zeros: <span class="hljs-built_in">int</span>
floating: <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>]
<span class="hljs-type">Memory</span> = <span class="hljs-type">Table</span>[<span class="hljs-built_in">int</span>, <span class="hljs-built_in">int</span>]
<span class="hljs-keyword">var</span>
mem: <span class="hljs-type">Memory</span>
mask: <span class="hljs-type">Mask</span>
<span class="hljs-keyword">proc</span> parseMask(text: <span class="hljs-built_in">string</span>): <span class="hljs-type">Mask</span> =
<span class="hljs-keyword">for</span> i, c <span class="hljs-keyword">in</span> text.reversed:
<span class="hljs-keyword">case</span> c
<span class="hljs-keyword">of</span> <span class="hljs-string">'0'</span>:
<span class="hljs-literal">result</span>.zeros += <span class="hljs-number">2</span> ^ i
<span class="hljs-keyword">of</span> <span class="hljs-string">'1'</span>:
<span class="hljs-literal">result</span>.ones += <span class="hljs-number">2</span> ^ i
<span class="hljs-keyword">of</span> <span class="hljs-string">'X'</span>:
<span class="hljs-literal">result</span>.floating.add i
<span class="hljs-keyword">else</span>:
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR unexpected character in mask string: "</span>, i, <span class="hljs-string">" "</span>, c
<span class="hljs-keyword">func</span> apply(n: <span class="hljs-built_in">int</span>; m: <span class="hljs-type">Mask</span>): <span class="hljs-built_in">int</span> =
<span class="hljs-literal">result</span> = n
setMask[<span class="hljs-built_in">int</span>](<span class="hljs-literal">result</span>, m.ones)
clearMask[<span class="hljs-built_in">int</span>](<span class="hljs-literal">result</span>, m.zeros)
mask = parseMask <span class="hljs-string">"XXXXXXXXXXXXXXXXXXXXXXXXXXXXX1XXXX0X"</span>
<span class="hljs-keyword">echo</span> mask
<span class="hljs-keyword">echo</span> <span class="hljs-number">11.</span>apply(mask) <span class="hljs-comment">## 73</span>
<span class="hljs-keyword">echo</span> <span class="hljs-number">101.</span>apply(mask)</code></pre>
<pre><samp>(ones: 64, zeros: 2, floating: @[0, 2, 3, 4, 5, 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])
73
101</samp></pre>
<p>Now let's parse full programming instructions with <code>startswith</code> and <code>scanf</code>.
I gotta say that I tend to forget the syntax of object variants (<code>case kind: T</code> sounds pretty special).</p>
<pre><code class="nim hljs"><span class="hljs-keyword">type</span>
<span class="hljs-type">Program</span> = <span class="hljs-built_in">seq</span>[<span class="hljs-type">Action</span>]
<span class="hljs-type">ActionKind</span> = <span class="hljs-keyword">enum</span>
updateMask, writeMem
<span class="hljs-type">Action</span> = <span class="hljs-keyword">object</span>
<span class="hljs-keyword">case</span> kind: <span class="hljs-type">ActionKind</span>
<span class="hljs-keyword">of</span> updateMask:
mask: <span class="hljs-type">Mask</span>
<span class="hljs-keyword">of</span> writeMem:
address: <span class="hljs-built_in">int</span>
value: <span class="hljs-built_in">int</span>
<span class="hljs-keyword">proc</span> parse(text: <span class="hljs-built_in">string</span>): <span class="hljs-type">Program</span> =
<span class="hljs-keyword">var</span> a: <span class="hljs-type">Action</span>
<span class="hljs-keyword">for</span> line <span class="hljs-keyword">in</span> text.splitLines:
<span class="hljs-keyword">if</span> line.startsWith(<span class="hljs-string">"mask"</span>):
a.kind = updateMask
a.mask = parseMask line[<span class="hljs-number">7</span> .. line.<span class="hljs-keyword">high</span>]
<span class="hljs-keyword">elif</span> line.startsWith(<span class="hljs-string">"mem"</span>):
a.kind = writeMem
<span class="hljs-keyword">if</span> <span class="hljs-keyword">not</span> scanf(line, <span class="hljs-string">"mem[$i] = $i"</span>, a.address, a.value):
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR parsing writeMem: "</span>, line
<span class="hljs-keyword">else</span>:
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR parsing line: "</span>, line
<span class="hljs-literal">result</span>.add a
<span class="hljs-keyword">let</span> example = <span class="hljs-string">"""mask = XXXXXXXXXXXXXXXXXXXXXXXXXXXXX1XXXX0X
mem[8] = 11
mem[7] = 101
mem[8] = 0"""</span>
<span class="hljs-keyword">let</span> exProg = parse example
<span class="hljs-keyword">echo</span> $exProg</code></pre>
<pre><samp>@[(kind: updateMask, mask: (ones: 64, zeros: 2, floating: @[0, 2, 3, 4, 5, 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])), (kind: writeMem, address: 8, value: 11), (kind: writeMem, address: 7, value: 101), (kind: writeMem, address: 8, value: 0)]</samp></pre>
<p>Last ingredient is the proc to run the Program on Cpu.</p>
<pre><code class="nim hljs"><span class="hljs-keyword">type</span>
<span class="hljs-type">Cpu</span> = <span class="hljs-keyword">object</span>
mask: <span class="hljs-type">Mask</span>
mem: <span class="hljs-type">Memory</span>
<span class="hljs-keyword">var</span> cpu: <span class="hljs-type">Cpu</span>
<span class="hljs-keyword">template</span> resetCpu() =
clear cpu.mem <span class="hljs-comment">## no need to reset mask as it is update as first action in program</span>
<span class="hljs-keyword">proc</span> run(cpu: <span class="hljs-keyword">var</span> <span class="hljs-type">Cpu</span>; p: <span class="hljs-type">Program</span>) =
<span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> p:
<span class="hljs-keyword">case</span> a.kind
<span class="hljs-keyword">of</span> updateMask:
cpu.mask = a.mask
<span class="hljs-keyword">of</span> writeMem:
cpu.mem[a.address] = a.value.apply(cpu.mask)
cpu.run exProg
<span class="hljs-keyword">echo</span> cpu
<span class="hljs-keyword">proc</span> answer(cpu: <span class="hljs-type">Cpu</span>): <span class="hljs-built_in">int</span> =
<span class="hljs-keyword">for</span> v <span class="hljs-keyword">in</span> cpu.mem.values:
<span class="hljs-literal">result</span> += v
<span class="hljs-keyword">echo</span> answer cpu
resetCpu
<span class="hljs-keyword">let</span> inProg = parse <span class="hljs-string">"2020/input14.txt"</span>.readFile
cpu.run inProg
<span class="hljs-keyword">echo</span> answer cpu</code></pre>
<pre><samp>(mask: (ones: 64, zeros: 2, floating: @[0, 2, 3, 4, 5, 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]), mem: {7: 101, 8: 64})
165
14925946402938</samp></pre>
<p>That's the right answer! You are <em class="star">one gold star</em> closer to saving your vacation.</p>
<p>for part 2:</p>
<ul>
<li>after refactoring mask code to parse floating bits (done above)</li>
<li><code>run2</code> proc below is straightforward</li>
<li><code>apply2</code> is the part that creates multiple addresses starting from a single address and a mask</li>
<li>finally <code>zeroBits</code> is the key ingredient that generates all floating bits combinations.</li>
</ul>
<p>At one point I did consider coding a recursive iterator, but apparently that is not possible,
see <a href="https://forum.nim-lang.org/t/5697">forum</a>.</p>
<pre><code class="nim hljs"><span class="hljs-keyword">iterator</span> zeroBits(s: <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>]): <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>] =
<span class="hljs-keyword">var</span> m: <span class="hljs-built_in">int</span>
<span class="hljs-keyword">var</span> t: <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>]
<span class="hljs-keyword">for</span> n <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> ..< <span class="hljs-number">2</span> ^ (s.len):
m = n
t = @[]
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0</span> .. s.<span class="hljs-keyword">high</span>:
<span class="hljs-keyword">if</span> m <span class="hljs-keyword">mod</span> <span class="hljs-number">2</span> == <span class="hljs-number">0</span>:
t.add s[i]
m = m <span class="hljs-keyword">shr</span> <span class="hljs-number">1</span>
<span class="hljs-keyword">yield</span> t
<span class="hljs-keyword">for</span> s <span class="hljs-keyword">in</span> zeroBits(@[<span class="hljs-number">1</span>, <span class="hljs-number">3</span>, <span class="hljs-number">5</span>]):
<span class="hljs-keyword">echo</span> s
<span class="hljs-keyword">func</span> apply2(a: <span class="hljs-built_in">int</span>; m: <span class="hljs-type">Mask</span>): <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>] =
<span class="hljs-keyword">var</span> b = a
setMask[<span class="hljs-built_in">int</span>](b, m.ones)
<span class="hljs-comment">## I ignore zeros part of the mask</span>
<span class="hljs-comment">## floating: loop over all possible combinations</span>
<span class="hljs-keyword">for</span> zeroBits <span class="hljs-keyword">in</span> zeroBits(m.floating):
<span class="hljs-keyword">var</span> c = b
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> m.floating:
<span class="hljs-keyword">if</span> i <span class="hljs-keyword">in</span> zeroBits:
c.clearBit(i)
<span class="hljs-keyword">else</span>:
c.setBit(i)
<span class="hljs-literal">result</span>.add c
<span class="hljs-keyword">let</span> exMask = parseMask(<span class="hljs-string">"000000000000000000000000000000X1001X"</span>)
<span class="hljs-keyword">echo</span> <span class="hljs-number">42.</span>apply2(exMask)</code></pre>
<pre><samp>@[1, 3, 5]
@[3, 5]
@[1, 5]
@[5]
@[1, 3]
@[3]
@[1]
@[]
@[26, 27, 58, 59]</samp></pre>
<p>looks good. let's apply directly to input without bothering about the example</p>
<pre><code class="nim hljs"><span class="hljs-keyword">proc</span> run2(cpu: <span class="hljs-keyword">var</span> <span class="hljs-type">Cpu</span>; p: <span class="hljs-type">Program</span>) =
<span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> p:
<span class="hljs-keyword">case</span> a.kind
<span class="hljs-keyword">of</span> updateMask:
cpu.mask = a.mask
<span class="hljs-keyword">of</span> writeMem:
<span class="hljs-keyword">for</span> address <span class="hljs-keyword">in</span> a.address.apply2(cpu.mask):
cpu.mem[address] = a.value
resetCpu
cpu.run2 inProg
<span class="hljs-keyword">echo</span> answer cpu</code></pre>
<pre><samp>3706820676200</samp></pre>
<p>That's the right answer! You are <em class="star">one gold star</em> closer to saving your vacation.</p>
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<pre><code class="nim hljs"><span class="hljs-keyword">import</span> nimib, animu, nimoji
nbInit
nbText: <span class="hljs-string">"""## 2020, Day 14: Docking Data :ship: :minidisc:
Today was an opportunity to learn more about [bitops](https://nim-lang.org/docs/bitops.html).
"""</span>.emojize
nbCode:
<span class="hljs-keyword">import</span> bitops, tables, algorithm, math, strscans, strutils
nbText: <span class="hljs-string">"For part 1 I first make sure I can parse the mask. `floating` field is a result of refactoring for part 2."</span>
nbCode:
<span class="hljs-keyword">type</span>
<span class="hljs-type">Mask</span> = <span class="hljs-keyword">object</span>
ones: <span class="hljs-built_in">int</span>
zeros: <span class="hljs-built_in">int</span>
floating: <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>]
<span class="hljs-type">Memory</span> = <span class="hljs-type">Table</span>[<span class="hljs-built_in">int</span>, <span class="hljs-built_in">int</span>]
<span class="hljs-keyword">var</span>
mem: <span class="hljs-type">Memory</span>
mask: <span class="hljs-type">Mask</span>
<span class="hljs-keyword">proc</span> parseMask(text: <span class="hljs-built_in">string</span>): <span class="hljs-type">Mask</span> =
<span class="hljs-keyword">for</span> i, c <span class="hljs-keyword">in</span> text.reversed:
<span class="hljs-keyword">case</span> c:
<span class="hljs-keyword">of</span> <span class="hljs-string">'0'</span>:
<span class="hljs-literal">result</span>.zeros += <span class="hljs-number">2</span>^i
<span class="hljs-keyword">of</span> <span class="hljs-string">'1'</span>:
<span class="hljs-literal">result</span>.ones += <span class="hljs-number">2</span>^i
<span class="hljs-keyword">of</span> <span class="hljs-string">'X'</span>:
<span class="hljs-literal">result</span>.floating.add i
<span class="hljs-keyword">else</span>:
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR unexpected character in mask string: "</span>, i, <span class="hljs-string">" "</span>, c
<span class="hljs-keyword">func</span> apply(n: <span class="hljs-built_in">int</span>, m: <span class="hljs-type">Mask</span>): <span class="hljs-built_in">int</span> =
<span class="hljs-literal">result</span> = n
setMask[<span class="hljs-built_in">int</span>](<span class="hljs-literal">result</span>, m.ones)
clearMask[<span class="hljs-built_in">int</span>](<span class="hljs-literal">result</span>, m.zeros)
mask = parseMask <span class="hljs-string">"XXXXXXXXXXXXXXXXXXXXXXXXXXXXX1XXXX0X"</span>
<span class="hljs-keyword">echo</span> mask
<span class="hljs-keyword">echo</span> <span class="hljs-number">11.</span>apply(mask) <span class="hljs-comment">## 73</span>
<span class="hljs-keyword">echo</span> <span class="hljs-number">101.</span>apply(mask) <span class="hljs-comment">## </span>
nbText: <span class="hljs-string">"""Now let's parse full programming instructions with `startswith` and `scanf`.
I gotta say that I tend to forget the syntax of object variants (`case kind: T` sounds pretty special).
"""</span>
nbCode:
<span class="hljs-keyword">type</span>
<span class="hljs-type">Program</span> = <span class="hljs-built_in">seq</span>[<span class="hljs-type">Action</span>] <span class="hljs-comment"># Action can go after</span>
<span class="hljs-type">ActionKind</span> = <span class="hljs-keyword">enum</span> updateMask, writeMem <span class="hljs-comment"># ActionKind apparently not</span>
<span class="hljs-type">Action</span> = <span class="hljs-keyword">object</span>
<span class="hljs-keyword">case</span> kind: <span class="hljs-type">ActionKind</span> <span class="hljs-comment"># I tend to forget the syntax </span>
<span class="hljs-keyword">of</span> updateMask:
mask: <span class="hljs-type">Mask</span>
<span class="hljs-keyword">of</span> writeMem:
address: <span class="hljs-built_in">int</span>
value: <span class="hljs-built_in">int</span>
<span class="hljs-keyword">proc</span> parse(text: <span class="hljs-built_in">string</span>): <span class="hljs-type">Program</span> =
<span class="hljs-keyword">var</span> a: <span class="hljs-type">Action</span>
<span class="hljs-keyword">for</span> line <span class="hljs-keyword">in</span> text.splitLines:
<span class="hljs-keyword">if</span> line.startsWith(<span class="hljs-string">"mask"</span>):
a.kind = updateMask
<span class="hljs-comment">#01234567</span>
<span class="hljs-comment">#mask = X</span>
a.mask = parseMask line[<span class="hljs-number">7.</span>.line.<span class="hljs-keyword">high</span>]
<span class="hljs-keyword">elif</span> line.startsWith(<span class="hljs-string">"mem"</span>):
a.kind = writeMem
<span class="hljs-keyword">if</span> <span class="hljs-keyword">not</span> scanf(line, <span class="hljs-string">"mem[$i] = $i"</span>, a.address, a.value):
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR parsing writeMem: "</span>, line
<span class="hljs-keyword">else</span>:
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR parsing line: "</span>, line
<span class="hljs-literal">result</span>.add a
<span class="hljs-keyword">let</span> example = <span class="hljs-string">"""mask = XXXXXXXXXXXXXXXXXXXXXXXXXXXXX1XXXX0X
mem[8] = 11
mem[7] = 101
mem[8] = 0"""</span>
<span class="hljs-keyword">let</span> exProg = parse example
<span class="hljs-keyword">echo</span> $exProg
nbText: <span class="hljs-string">"Last ingredient is the proc to run the Program on Cpu."</span>
nbCode:
<span class="hljs-keyword">type</span>
<span class="hljs-type">Cpu</span> = <span class="hljs-keyword">object</span>
mask: <span class="hljs-type">Mask</span>
mem: <span class="hljs-type">Memory</span>
<span class="hljs-keyword">var</span> cpu: <span class="hljs-type">Cpu</span>
<span class="hljs-keyword">template</span> resetCpu =
clear cpu.mem <span class="hljs-comment">## no need to reset mask as it is update as first action in program</span>
<span class="hljs-keyword">proc</span> run(cpu: <span class="hljs-keyword">var</span> <span class="hljs-type">Cpu</span>, p: <span class="hljs-type">Program</span>) =
<span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> p:
<span class="hljs-keyword">case</span> a.kind:
<span class="hljs-keyword">of</span> updateMask:
cpu.mask = a.mask
<span class="hljs-keyword">of</span> writeMem:
cpu.mem[a.address] = a.value.apply(cpu.mask)
cpu.run exProg
<span class="hljs-keyword">echo</span> cpu
<span class="hljs-keyword">proc</span> answer(cpu: <span class="hljs-type">Cpu</span>): <span class="hljs-built_in">int</span> =
<span class="hljs-keyword">for</span> v <span class="hljs-keyword">in</span> cpu.mem.values:
<span class="hljs-literal">result</span> += v
<span class="hljs-keyword">echo</span> answer cpu
resetCpu
<span class="hljs-keyword">let</span> inProg = parse <span class="hljs-string">"2020/input14.txt"</span>.readFile
cpu.run inProg
<span class="hljs-keyword">echo</span> answer cpu
gotTheStar
nbText: <span class="hljs-string">"""for part 2:
* after refactoring mask code to parse floating bits (done above)
* `run2` proc below is straightforward
* `apply2` is the part that creates multiple addresses starting from a single address and a mask
* finally `zeroBits` is the key ingredient that generates all floating bits combinations.
At one point I did consider coding a recursive iterator, but apparently that is not possible,
see [forum](https://forum.nim-lang.org/t/5697).
"""</span>
nbCode:
<span class="hljs-keyword">iterator</span> zeroBits(s: <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>]): <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>] =
<span class="hljs-keyword">var</span> m: <span class="hljs-built_in">int</span>
<span class="hljs-keyword">var</span> t:<span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>]
<span class="hljs-keyword">for</span> n <span class="hljs-keyword">in</span> <span class="hljs-number">0.</span>.<<span class="hljs-number">2</span>^(s.len):
m = n
t = @[]
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0.</span>.s.<span class="hljs-keyword">high</span>:
<span class="hljs-keyword">if</span> m <span class="hljs-keyword">mod</span> <span class="hljs-number">2</span> == <span class="hljs-number">0</span>:
t.add s[i]
m = m <span class="hljs-keyword">shr</span> <span class="hljs-number">1</span>
<span class="hljs-keyword">yield</span> t
<span class="hljs-keyword">for</span> s <span class="hljs-keyword">in</span> zeroBits(@[<span class="hljs-number">1</span>, <span class="hljs-number">3</span>, <span class="hljs-number">5</span>]):
<span class="hljs-keyword">echo</span> s
<span class="hljs-keyword">func</span> apply2(a: <span class="hljs-built_in">int</span>, m: <span class="hljs-type">Mask</span>): <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>] =
<span class="hljs-keyword">var</span> b = a
setMask[<span class="hljs-built_in">int</span>](b, m.ones)
<span class="hljs-comment">## I ignore zeros part of the mask</span>
<span class="hljs-comment">## floating: loop over all possible combinations</span>
<span class="hljs-keyword">for</span> zeroBits <span class="hljs-keyword">in</span> zeroBits(m.floating):
<span class="hljs-keyword">var</span> c = b
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> m.floating:
<span class="hljs-keyword">if</span> i <span class="hljs-keyword">in</span> zeroBits:
c.clearBit(i)
<span class="hljs-keyword">else</span>:
c.setBit(i)
<span class="hljs-literal">result</span>.add c
<span class="hljs-keyword">let</span> exMask = parseMask(<span class="hljs-string">"000000000000000000000000000000X1001X"</span>)
<span class="hljs-keyword">echo</span> <span class="hljs-number">42.</span>apply2(exMask)
nbText: <span class="hljs-string">"looks good. let's apply directly to input without bothering about the example"</span>
nbCode:
<span class="hljs-keyword">proc</span> run2(cpu: <span class="hljs-keyword">var</span> <span class="hljs-type">Cpu</span>, p: <span class="hljs-type">Program</span>) =
<span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> p:
<span class="hljs-keyword">case</span> a.kind:
<span class="hljs-keyword">of</span> updateMask:
cpu.mask = a.mask
<span class="hljs-keyword">of</span> writeMem:
<span class="hljs-keyword">for</span> address <span class="hljs-keyword">in</span> a.address.apply2(cpu.mask):
cpu.mem[address] = a.value
resetCpu
cpu.run2 inProg
<span class="hljs-keyword">echo</span> answer cpu
gotTheStar
nbSave</code></pre>
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