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<title>2020\day08.nim</title>
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<span><a href="..">🏡</a></span>
<span><code>2020\day08.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 8: Handheld Halting</h1>
<p>For a better solution than mine look at the solution shared
by fxn on the forum (<a href="https://gist.github.com/fxn/bbd90877bcd27581ee5f7720495c3c3f">gist</a>).</p>
<p>I use a inelegant global trace (instead of an <code>intsets</code> of visted indices).
This solution is not that bad anyway.</p>
<p>Listing the imports (usually I hide them from the document).</p>
<pre><code class="nim hljs"><span class="hljs-keyword">import</span>
strutils, parseutils, strformat, std / enumerate</code></pre>
<p>rather standard types. I regretted very soon naming instructions
in the program as <code>instrs</code>, what a bad name!</p>
<pre><code class="nim hljs"><span class="hljs-keyword">type</span>
<span class="hljs-type">OpCode</span> = <span class="hljs-keyword">enum</span>
opNop = <span class="hljs-string">"nop"</span>, opAcc = <span class="hljs-string">"acc"</span>, opJmp = <span class="hljs-string">"jmp"</span>
<span class="hljs-type">Instruction</span> = <span class="hljs-keyword">tuple</span>[op: <span class="hljs-type">OpCode</span>, val: <span class="hljs-built_in">int</span>]
<span class="hljs-type">Program</span> = <span class="hljs-keyword">object</span>
tr: <span class="hljs-built_in">int</span> <span class="hljs-comment">## p.tr: pointer</span>
acc: <span class="hljs-built_in">int</span> <span class="hljs-comment">## global register</span>
instrs: <span class="hljs-built_in">seq</span>[<span class="hljs-type">Instruction</span>]
<span class="hljs-type">Trace</span> = <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>]]</code></pre>
<p>the parsing is clean, since opcodes are 3 letters do not even need scanf (enumerate is used for debugging)</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-type">Instruction</span>] =
<span class="hljs-keyword">var</span>
op: <span class="hljs-type">OpCode</span>
val: <span class="hljs-built_in">int</span>
<span class="hljs-keyword">for</span> i, line <span class="hljs-keyword">in</span> enumerate(text.splitLines):
<span class="hljs-keyword">try</span>:
op = parseEnum[<span class="hljs-type">OpCode</span>](line[<span class="hljs-number">0</span> .. <span class="hljs-number">2</span>])
<span class="hljs-keyword">discard</span> parseInt(line[<span class="hljs-number">4</span> .. ^<span class="hljs-number">1</span>], val)
<span class="hljs-literal">result</span>.add (op, val)
<span class="hljs-keyword">except</span>:
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR parsing "</span>, i, <span class="hljs-string">" "</span>, line</code></pre>
<p>testing the first lines of code on the example</p>
<pre><code class="nim hljs"><span class="hljs-keyword">let</span> example = <span class="hljs-string">"""nop +0
acc +1
jmp +4
acc +3
jmp -3
acc -99
acc +1
jmp -4
acc +6"""</span>
<span class="hljs-keyword">var</span> exp = <span class="hljs-type">Program</span>(instrs: parse example)
<span class="hljs-keyword">echo</span> exp</code></pre>
<pre><samp>(tr: 0, acc: 0, instrs: @[(op: nop, val: 0), (op: acc, val: 1), (op: jmp, val: 4), (op: acc, val: 3), (op: jmp, val: -3), (op: acc, val: -99), (op: acc, val: 1), (op: jmp, val: -4), (op: acc, val: 6)])</samp></pre>
<p>as mentioned, I decided to go with a global trace variable for simplicty</p>
<pre><code class="nim hljs"><span class="hljs-keyword">proc</span> initTrace(p: <span class="hljs-type">Program</span>): <span class="hljs-type">Trace</span> =
<span class="hljs-literal">result</span>.setlen(p.instrs.len)
<span class="hljs-literal">result</span>[p.tr].add <span class="hljs-number">1</span>
<span class="hljs-keyword">var</span> tr = initTrace(exp)
<span class="hljs-keyword">echo</span> tr
<span class="hljs-keyword">template</span> trace(): <span class="hljs-built_in">bool</span> =
tr[p.tr].add(i + <span class="hljs-number">1</span>)
tr[p.tr].len == <span class="hljs-number">1</span> <span class="hljs-comment">## somewhat cryptic. If you visited more than once length will be 2</span></code></pre>
<pre><samp>@[@[1], @[], @[], @[], @[], @[], @[], @[], @[]]</samp></pre>
<p>and here is the code for the execution of the program (single step)</p>
<pre><code class="nim hljs"><span class="hljs-keyword">proc</span> op(p: <span class="hljs-type">Program</span>): <span class="hljs-type">OpCode</span> =
p.instrs[p.tr].op
<span class="hljs-keyword">proc</span> val(p: <span class="hljs-type">Program</span>): <span class="hljs-built_in">int</span> =
p.instrs[p.tr].val
<span class="hljs-keyword">proc</span> endd(p: <span class="hljs-type">Program</span>): <span class="hljs-built_in">bool</span> =
(p.tr == p.instrs.len) <span class="hljs-comment">## end is keyword</span>
<span class="hljs-keyword">proc</span> exec(p: <span class="hljs-keyword">var</span> <span class="hljs-type">Program</span>): <span class="hljs-built_in">bool</span> =
<span class="hljs-keyword">let</span> i = tr[p.tr][^<span class="hljs-number">1</span>]
<span class="hljs-keyword">case</span> p.op
<span class="hljs-keyword">of</span> opNop:
inc p.tr
<span class="hljs-keyword">of</span> opAcc:
p.acc += p.val
inc p.tr
<span class="hljs-keyword">of</span> opJmp:
inc p.tr, p.val
<span class="hljs-keyword">if</span> p.endd:
<span class="hljs-keyword">return</span> <span class="hljs-literal">false</span>
trace</code></pre>
<p>this was a template at the beginning
but I forgot strformat has known <a href="https://nim-lang.org/docs/strformat.html#limitations">limitations with template arguments</a>.</p>
<p>Of this I do like the name <code>echoo</code> (this is throwaway stuff for debugging purposes).</p>
<pre><code class="nim hljs"><span class="hljs-keyword">proc</span> echoo(p: <span class="hljs-type">Program</span>; tr: <span class="hljs-type">Trace</span>) =
<span class="hljs-keyword">echo</span> p.op, <span class="hljs-string">" "</span>, <span class="hljs-string">fmt"{p.val:3}"</span>, <span class="hljs-string">" | "</span>, tr[p.tr]
<span class="hljs-keyword">discard</span>
echoo(exp, tr)
<span class="hljs-keyword">while</span> exec(exp):
echoo(exp, tr)
echoo(exp, tr)
<span class="hljs-keyword">echo</span> <span class="hljs-string">"part1: "</span>, exp.acc <span class="hljs-comment">## 5, ok</span>
exp.acc = <span class="hljs-number">0</span> <span class="hljs-comment">## reset for part2</span></code></pre>
<pre><samp>nop 0 | @[1]
acc 1 | @[2]
jmp 4 | @[3]
acc 1 | @[4]
jmp -4 | @[5]
acc 3 | @[6]
jmp -3 | @[7]
acc 1 | @[2, 8]
part1: 5</samp></pre>
<p>part 2 appears first for the example. It is straightforward test of fixing iteratively all positions</p>
<pre><code class="nim hljs"><span class="hljs-keyword">var</span> q: <span class="hljs-type">Program</span>
<span class="hljs-keyword">var</span> k: <span class="hljs-built_in">int</span>
<span class="hljs-keyword">template</span> fix(p: <span class="hljs-type">Program</span>) =
k = <span class="hljs-number">0</span>
q = p
<span class="hljs-keyword">while</span> <span class="hljs-keyword">not</span> q.endd:
q = p
<span class="hljs-keyword">if</span> q.acc != <span class="hljs-number">0</span>:
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR it should be zero!"</span>
<span class="hljs-keyword">while</span> p.instrs[k].op == opAcc:
inc k
<span class="hljs-keyword">if</span> p.instrs[k].op == opJmp:
q.instrs[k].op = opNop
<span class="hljs-keyword">elif</span> p.instrs[k].op == opNop:
q.instrs[k].op = opJmp
<span class="hljs-keyword">else</span>:
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR should not be here"</span>
<span class="hljs-comment">## echo "trying to fix instruction ", k</span>
tr = initTrace(q)
<span class="hljs-comment">## echo "q.acc: ", q.acc</span>
<span class="hljs-keyword">while</span> exec(q):
<span class="hljs-keyword">discard</span>
inc k
<span class="hljs-keyword">echo</span> <span class="hljs-string">"part2: "</span>, q.acc
fix exp <span class="hljs-comment">## 8, ok</span></code></pre>
<pre><samp>part2: 8</samp></pre>
<p>Finally let's collect the stars!</p>
<pre><code class="nim hljs"><span class="hljs-keyword">let</span> input = <span class="hljs-string">"2020/input08.txt"</span>.readFile
<span class="hljs-keyword">var</span> inp = <span class="hljs-type">Program</span>(instrs: parse input)
tr = initTrace(inp)
<span class="hljs-keyword">while</span> exec(inp):
<span class="hljs-keyword">discard</span>
<span class="hljs-keyword">echo</span> <span class="hljs-string">"part1: "</span>, inp.acc <span class="hljs-comment">## 1810</span>
tr = initTrace(inp)
inp.acc = <span class="hljs-number">0</span>
inp.tr = <span class="hljs-number">0</span>
fix inp <span class="hljs-comment">## 969</span></code></pre>
<pre><samp>part1: 1810
part2: 969</samp></pre>
<p>you know your solution is bad when trying to publish it you incur in all sorts of bugs...</p>
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<pre><code class="nim hljs"><span class="hljs-keyword">import</span> nimib, animu
nbInit
nbText: <span class="hljs-string">"# 2020, Day 8: Handheld Halting"</span>
nbText: <span class="hljs-string">"""For a better solution than mine look at the solution shared
by fxn on the forum ([gist](https://gist.github.com/fxn/bbd90877bcd27581ee5f7720495c3c3f)).
I use a inelegant global trace (instead of an `intsets` of visted indices).
This solution is not that bad anyway.
Listing the imports (usually I hide them from the document).
"""</span>
nbCode:
<span class="hljs-keyword">import</span> strutils, parseutils, strformat, std/enumerate
nbText: <span class="hljs-string">"""rather standard types. I regretted very soon naming instructions
in the program as `instrs`, what a bad name!"""</span>
nbCode:
<span class="hljs-keyword">type</span>
<span class="hljs-type">OpCode</span> = <span class="hljs-keyword">enum</span>
opNop = <span class="hljs-string">"nop"</span>, opAcc = <span class="hljs-string">"acc"</span>, opJmp = <span class="hljs-string">"jmp"</span>
<span class="hljs-type">Instruction</span> = <span class="hljs-keyword">tuple</span>[op: <span class="hljs-type">OpCode</span>, val: <span class="hljs-built_in">int</span>]
<span class="hljs-type">Program</span> = <span class="hljs-keyword">object</span>
tr: <span class="hljs-built_in">int</span> <span class="hljs-comment">## p.tr: pointer</span>
acc: <span class="hljs-built_in">int</span> <span class="hljs-comment">## global register</span>
instrs: <span class="hljs-built_in">seq</span>[<span class="hljs-type">Instruction</span>]
<span class="hljs-type">Trace</span> = <span class="hljs-built_in">seq</span>[<span class="hljs-built_in">seq</span>[<span class="hljs-built_in">int</span>]]
nbText: <span class="hljs-string">"the parsing is clean, since opcodes are 3 letters do not even need scanf (enumerate is used for debugging)"</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-type">Instruction</span>] =
<span class="hljs-keyword">var</span>
op: <span class="hljs-type">OpCode</span>
val: <span class="hljs-built_in">int</span>
<span class="hljs-keyword">for</span> i, line <span class="hljs-keyword">in</span> enumerate(text.splitLines):
<span class="hljs-keyword">try</span>:
op = parseEnum[<span class="hljs-type">OpCode</span>](line[<span class="hljs-number">0</span> .. <span class="hljs-number">2</span>])
<span class="hljs-keyword">discard</span> parseInt(line[<span class="hljs-number">4</span> .. ^<span class="hljs-number">1</span>], val)
<span class="hljs-literal">result</span>.add (op, val)
<span class="hljs-keyword">except</span>:
<span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR parsing "</span>, i, <span class="hljs-string">" "</span>, line
nbText: <span class="hljs-string">"testing the first lines of code on the example"</span>
nbCode:
<span class="hljs-keyword">let</span> example = <span class="hljs-string">"""nop +0
acc +1
jmp +4
acc +3
jmp -3
acc -99
acc +1
jmp -4
acc +6"""</span>
<span class="hljs-keyword">var</span> exp = <span class="hljs-type">Program</span>(instrs: parse example)
<span class="hljs-keyword">echo</span> exp
nbText: <span class="hljs-string">"as mentioned, I decided to go with a global trace variable for simplicty"</span>
nbCode:
<span class="hljs-keyword">proc</span> initTrace(p: <span class="hljs-type">Program</span>): <span class="hljs-type">Trace</span> =
<span class="hljs-literal">result</span>.setlen(p.instrs.len)
<span class="hljs-literal">result</span>[p.tr].add <span class="hljs-number">1</span>
<span class="hljs-comment"># I will keep it global</span>
<span class="hljs-keyword">var</span> tr = initTrace(exp)
<span class="hljs-keyword">echo</span> tr
<span class="hljs-keyword">template</span> trace: <span class="hljs-built_in">bool</span> =
tr[p.tr].add(i + <span class="hljs-number">1</span>)
tr[p.tr].len == <span class="hljs-number">1</span> <span class="hljs-comment">## somewhat cryptic. If you visited more than once length will be 2</span>
nbText: <span class="hljs-string">"and here is the code for the execution of the program (single step)"</span>
nbCode:
<span class="hljs-keyword">proc</span> op(p: <span class="hljs-type">Program</span>): <span class="hljs-type">OpCode</span> = p.instrs[p.tr].op
<span class="hljs-keyword">proc</span> val(p: <span class="hljs-type">Program</span>): <span class="hljs-built_in">int</span> = p.instrs[p.tr].val
<span class="hljs-keyword">proc</span> endd(p: <span class="hljs-type">Program</span>): <span class="hljs-built_in">bool</span> = (p.tr == p.instrs.len) <span class="hljs-comment">## end is keyword</span>
<span class="hljs-keyword">proc</span> exec(p: <span class="hljs-keyword">var</span> <span class="hljs-type">Program</span>): <span class="hljs-built_in">bool</span> =
<span class="hljs-keyword">let</span>
i = tr[p.tr][^<span class="hljs-number">1</span>]
<span class="hljs-keyword">case</span> p.op:
<span class="hljs-keyword">of</span> opNop:
inc p.tr
<span class="hljs-keyword">of</span> opAcc:
p.acc += p.val
inc p.tr
<span class="hljs-keyword">of</span> opJmp:
inc p.tr, p.val
<span class="hljs-keyword">if</span> p.endd:
<span class="hljs-keyword">return</span> <span class="hljs-literal">false</span>
trace
nbText: <span class="hljs-string">"""this was a template at the beginning
but I forgot strformat has known [limitations with template arguments](https://nim-lang.org/docs/strformat.html#limitations).
Of this I do like the name `echoo` (this is throwaway stuff for debugging purposes).
"""</span>
nbCode:
<span class="hljs-keyword">proc</span> echoo(p: <span class="hljs-type">Program</span>, tr: <span class="hljs-type">Trace</span>) =
<span class="hljs-keyword">echo</span> p.op, <span class="hljs-string">" "</span>, <span class="hljs-string">fmt"{p.val:3}"</span>, <span class="hljs-string">" | "</span>, tr[p.tr]
<span class="hljs-keyword">discard</span>
echoo(exp, tr)
<span class="hljs-keyword">while</span> exec(exp): echoo(exp, tr)
echoo(exp, tr)
<span class="hljs-keyword">echo</span> <span class="hljs-string">"part1: "</span>, exp.acc <span class="hljs-comment">## 5, ok</span>
exp.acc = <span class="hljs-number">0</span> <span class="hljs-comment">## reset for part2</span>
nbText: <span class="hljs-string">"part 2 appears first for the example. It is straightforward test of fixing iteratively all positions"</span>
nbCode:
<span class="hljs-comment"># part 2 fix (example first)</span>
<span class="hljs-keyword">var</span> q: <span class="hljs-type">Program</span>
<span class="hljs-keyword">var</span> k: <span class="hljs-built_in">int</span> <span class="hljs-comment"># last operation to test fixing</span>
<span class="hljs-keyword">template</span> fix(p: <span class="hljs-type">Program</span>) =
k = <span class="hljs-number">0</span>
q = p
<span class="hljs-keyword">while</span> <span class="hljs-keyword">not</span> q.endd:
q = p
<span class="hljs-keyword">if</span> q.acc != <span class="hljs-number">0</span>: <span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR it should be zero!"</span>
<span class="hljs-keyword">while</span> p.instrs[k].op == opAcc: inc k
<span class="hljs-keyword">if</span> p.instrs[k].op == opJmp: q.instrs[k].op = opNop
<span class="hljs-keyword">elif</span> p.instrs[k].op == opNop: q.instrs[k].op = opJmp
<span class="hljs-keyword">else</span>: <span class="hljs-keyword">echo</span> <span class="hljs-string">"ERROR should not be here"</span>
<span class="hljs-comment">##echo "trying to fix instruction ", k</span>
tr = initTrace(q)
<span class="hljs-comment">##echo "q.acc: ", q.acc</span>
<span class="hljs-keyword">while</span> exec(q): <span class="hljs-keyword">discard</span>
inc k
<span class="hljs-keyword">echo</span> <span class="hljs-string">"part2: "</span>, q.acc
fix exp <span class="hljs-comment">## 8, ok</span>
nbText: <span class="hljs-string">"Finally let's collect the stars!"</span>
nbCode:
<span class="hljs-keyword">let</span> input = <span class="hljs-string">"2020/input08.txt"</span>.readFile
<span class="hljs-keyword">var</span> inp = <span class="hljs-type">Program</span>(instrs: parse input)
tr = initTrace(inp)
<span class="hljs-keyword">while</span> exec(inp): <span class="hljs-keyword">discard</span>
<span class="hljs-keyword">echo</span> <span class="hljs-string">"part1: "</span>, inp.acc <span class="hljs-comment">## 1810</span>
tr = initTrace(inp)
inp.acc = <span class="hljs-number">0</span>
inp.tr = <span class="hljs-number">0</span>
fix inp <span class="hljs-comment">## 969</span>
nbText: <span class="hljs-string">"you know your solution is bad when trying to publish it you incur in all sorts of bugs..."</span>
nbSave</code></pre>
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