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|
<!DOCTYPE html>
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<meta name="description" content="PHPerKaigi 2022 で私が作成した PHPer チャレンジ問題を解説する。">
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<title>PHPerKaigi 2022 トークン問題の解説 | REPL: Rest-Eat-Program Loop</title>
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<a href="/">REPL: Rest-Eat-Program Loop</a>
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<main class="main">
<article class="post-single">
<header class="post-header">
<h1 class="post-title">PHPerKaigi 2022 トークン問題の解説</h1>
<ul class="post-tags">
<li class="tag">
<a href="/tags/conference/">カンファレンス</a>
</li>
<li class="tag">
<a href="/tags/php/">PHP</a>
</li>
<li class="tag">
<a href="/tags/phperkaigi/">PHPerKaigi</a>
</li>
</ul>
</header>
<div class="post-content">
<section>
<h2 id="changelog">更新履歴</h2>
<ol>
<li class="revision">
<time datetime="2022-04-09">2022-04-09</time>: 公開
</li>
<li class="revision">
<time datetime="2022-04-16">2022-04-16</time>: 2問目、3問目の解説を追加、1問目に加筆
</li>
</ol>
</section>
<section class="section-1">
<h2 id="" class="section-header">
はじめに
</h2>
<div class="section-body">
<div class="paragraph">
<p>本日開始された <a href="https://phperkaigi.jp/2022/">PHPerKaigi 2022</a> の PHPer
チャレンジにおいて、弊社
<a href="https://www.dgcircus.com/">デジタルサーカス株式会社</a> の問題を
3問作成した。この記事では、これらの問題の解説をおこなう。</p>
</div>
<div class="paragraph">
<p>リポジトリはこちら: <a href="https://github.com/nsfisis/PHPerKaigi2022-tokens" class="bare">https://github.com/nsfisis/PHPerKaigi2022-tokens</a></p>
</div>
</div>
</section>
<section class="section-1">
<h2 id="" class="section-header">
第1問 brainf_ck.php
</h2>
<div class="section-body">
<div class="paragraph">
<p>ソースコードはこちら。実行には PHP 8.1 以上が必要なので注意。</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"><span class="o"><?</span><span class="n">php</span>
<span class="k">declare</span><span class="p">(</span><span class="n">strict_types</span><span class="o">=</span><span class="mi">0</span><span class="no">O1</span><span class="p">);</span>
<span class="kn">namespace</span> <span class="nn">Dgcircus\PHPerKaigi\Y2022</span><span class="p">;</span>
<span class="cd">/**
* @todo
* Run this program to acquire a PHPer token.
*/</span>
<span class="n">https</span><span class="o">://</span><span class="n">creativecommons</span><span class="mf">.</span><span class="n">org</span><span class="o">/</span><span class="n">publicdomain</span><span class="o">/</span><span class="n">zero</span><span class="o">/</span><span class="mf">1.0</span><span class="o">/</span>
<span class="err">\</span><span class="nb">error_reporting</span><span class="p">(</span><span class="o">~+!</span><span class="s1">'We are hiring!'</span><span class="p">);</span>
<span class="nv">$z</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$f</span><span class="p">)</span> <span class="o">=></span> <span class="p">(</span><span class="k">fn</span><span class="p">(</span><span class="nv">$x</span><span class="p">)</span> <span class="o">=></span> <span class="nv">$f</span><span class="p">(</span><span class="k">fn</span><span class="p">(...</span><span class="nv">$xs</span><span class="p">)</span> <span class="o">=></span> <span class="nv">$x</span><span class="p">(</span><span class="nv">$x</span><span class="p">)(</span><span class="mf">...</span><span class="nv">$xs</span><span class="p">)))(</span><span class="k">fn</span><span class="p">(</span><span class="nv">$x</span><span class="p">)</span> <span class="o">=></span> <span class="nv">$f</span><span class="p">(</span><span class="k">fn</span><span class="p">(...</span><span class="nv">$xs</span><span class="p">)</span> <span class="o">=></span> <span class="nv">$x</span><span class="p">(</span><span class="nv">$x</span><span class="p">)(</span><span class="mf">...</span><span class="nv">$xs</span><span class="p">)));</span>
<span class="nv">$id</span> <span class="o">=</span> <span class="err">\</span><span class="nb">spl_object_id</span><span class="p">(</span><span class="mf">...</span><span class="p">);</span>
<span class="nv">$put</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$c</span><span class="p">)</span> <span class="o">=></span> <span class="err">\</span><span class="nb">printf</span><span class="p">(</span><span class="s1">'%c'</span><span class="p">,</span> <span class="nv">$c</span><span class="p">);</span>
<span class="nv">$mm</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$p</span><span class="p">,</span> <span class="nv">$n</span><span class="p">)</span> <span class="o">=></span> <span class="k">new</span> <span class="err">\</span><span class="nf">ArrayObject</span><span class="p">(</span><span class="err">\</span><span class="nb">array_fill</span><span class="p">(</span><span class="o">+!!</span><span class="p">[],</span> <span class="nv">$n</span><span class="p">,</span> <span class="nv">$p</span><span class="p">));</span>
<span class="err">$👉</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="nv">$mp</span><span class="p">,</span> <span class="nv">$pc</span><span class="p">)</span> <span class="o">=></span> <span class="p">[</span><span class="o">++</span><span class="nv">$mp</span><span class="p">,</span> <span class="o">++</span><span class="nv">$pc</span><span class="p">];</span>
<span class="err">$👈</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="nv">$mp</span><span class="p">,</span> <span class="nv">$pc</span><span class="p">)</span> <span class="o">=></span> <span class="p">[</span><span class="o">--</span><span class="nv">$mp</span><span class="p">,</span> <span class="o">++</span><span class="nv">$pc</span><span class="p">];</span>
<span class="err">$👍</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="nv">$mp</span><span class="p">,</span> <span class="nv">$pc</span><span class="p">)</span> <span class="o">=></span> <span class="p">[</span><span class="nv">$mp</span><span class="p">,</span> <span class="o">++</span><span class="nv">$pc</span><span class="p">,</span> <span class="o">++</span><span class="nv">$m</span><span class="p">[</span><span class="nv">$mp</span><span class="p">]];</span>
<span class="err">$👎</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="nv">$mp</span><span class="p">,</span> <span class="nv">$pc</span><span class="p">)</span> <span class="o">=></span> <span class="p">[</span><span class="nv">$mp</span><span class="p">,</span> <span class="o">++</span><span class="nv">$pc</span><span class="p">,</span> <span class="o">--</span><span class="nv">$m</span><span class="p">[</span><span class="nv">$mp</span><span class="p">]];</span>
<span class="err">$📝</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="nv">$mp</span><span class="p">,</span> <span class="nv">$pc</span><span class="p">)</span> <span class="o">=></span> <span class="p">[</span><span class="nv">$mp</span><span class="p">,</span> <span class="o">++</span><span class="nv">$pc</span><span class="p">,</span> <span class="nv">$put</span><span class="p">(</span><span class="nv">$m</span><span class="p">[</span><span class="nv">$mp</span><span class="p">])];</span>
<span class="err">$🤡</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="nv">$mp</span><span class="p">,</span> <span class="nv">$pc</span><span class="p">)</span> <span class="o">=></span> <span class="k">match</span> <span class="p">(</span><span class="nv">$m</span><span class="p">[</span><span class="nv">$mp</span><span class="p">])</span> <span class="p">{</span>
<span class="o">+!!</span><span class="p">[]</span> <span class="o">=></span> <span class="p">[</span><span class="nv">$mp</span><span class="p">,</span> <span class="nv">$z</span><span class="p">(</span><span class="k">fn</span><span class="p">(</span><span class="nv">$loop</span><span class="p">)</span> <span class="o">=></span> <span class="k">fn</span><span class="p">(</span><span class="nv">$pc</span><span class="p">,</span> <span class="nv">$n</span><span class="p">)</span> <span class="o">=></span> <span class="k">match</span> <span class="p">(</span><span class="nv">$id</span><span class="p">(</span><span class="nv">$p</span><span class="p">[</span><span class="nv">$pc</span><span class="p">]))</span> <span class="p">{</span>
<span class="nv">$b</span> <span class="o">=></span> <span class="nv">$loop</span><span class="p">(</span><span class="o">++</span><span class="nv">$pc</span><span class="p">,</span> <span class="o">++</span><span class="nv">$n</span><span class="p">),</span>
<span class="nv">$e</span> <span class="o">=></span> <span class="nv">$n</span> <span class="o">===</span> <span class="o">+!!</span><span class="p">[]</span> <span class="o">?</span> <span class="o">++</span><span class="nv">$pc</span> <span class="o">:</span> <span class="nv">$loop</span><span class="p">(</span><span class="o">++</span><span class="nv">$pc</span><span class="p">,</span> <span class="o">--</span><span class="nv">$n</span><span class="p">),</span>
<span class="k">default</span> <span class="o">=></span> <span class="nv">$loop</span><span class="p">(</span><span class="o">++</span><span class="nv">$pc</span><span class="p">,</span> <span class="nv">$n</span><span class="p">),</span>
<span class="p">})(</span><span class="nv">$pc</span><span class="p">,</span> <span class="o">-!</span><span class="p">[])],</span>
<span class="k">default</span> <span class="o">=></span> <span class="p">[</span><span class="nv">$mp</span><span class="p">,</span> <span class="o">++</span><span class="nv">$pc</span><span class="p">],</span>
<span class="p">};</span>
<span class="err">$🎪</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="nv">$mp</span><span class="p">,</span> <span class="nv">$pc</span><span class="p">)</span> <span class="o">=></span> <span class="k">match</span> <span class="p">(</span><span class="nv">$m</span><span class="p">[</span><span class="nv">$mp</span><span class="p">])</span> <span class="p">{</span>
<span class="o">+!!</span><span class="p">[]</span> <span class="o">=></span> <span class="p">[</span><span class="nv">$mp</span><span class="p">,</span> <span class="o">++</span><span class="nv">$pc</span><span class="p">],</span>
<span class="k">default</span> <span class="o">=></span> <span class="p">[</span><span class="nv">$mp</span><span class="p">,</span> <span class="nv">$z</span><span class="p">(</span><span class="k">fn</span><span class="p">(</span><span class="nv">$loop</span><span class="p">)</span> <span class="o">=></span> <span class="k">fn</span><span class="p">(</span><span class="nv">$pc</span><span class="p">,</span> <span class="nv">$n</span><span class="p">)</span> <span class="o">=></span> <span class="k">match</span> <span class="p">(</span><span class="nv">$id</span><span class="p">(</span><span class="nv">$p</span><span class="p">[</span><span class="nv">$pc</span><span class="p">]))</span> <span class="p">{</span>
<span class="nv">$e</span> <span class="o">=></span> <span class="nv">$loop</span><span class="p">(</span><span class="o">--</span><span class="nv">$pc</span><span class="p">,</span> <span class="o">++</span><span class="nv">$n</span><span class="p">),</span>
<span class="nv">$b</span> <span class="o">=></span> <span class="nv">$n</span> <span class="o">===</span> <span class="o">+!!</span><span class="p">[]</span> <span class="o">?</span> <span class="nv">$pc</span><span class="o">+!</span><span class="p">[]</span> <span class="o">:</span> <span class="nv">$loop</span><span class="p">(</span><span class="o">--</span><span class="nv">$pc</span><span class="p">,</span> <span class="o">--</span><span class="nv">$n</span><span class="p">),</span>
<span class="k">default</span> <span class="o">=></span> <span class="nv">$loop</span><span class="p">(</span><span class="o">--</span><span class="nv">$pc</span><span class="p">,</span> <span class="nv">$n</span><span class="p">),</span>
<span class="p">})(</span><span class="nv">$pc</span><span class="p">,</span> <span class="o">-!</span><span class="p">[])],</span>
<span class="p">};</span>
<span class="err">$🐘</span> <span class="o">=</span> <span class="k">fn</span><span class="p">(</span><span class="nv">$p</span><span class="p">)</span> <span class="o">=></span> <span class="nv">$z</span><span class="p">(</span><span class="k">fn</span><span class="p">(</span><span class="nv">$loop</span><span class="p">)</span> <span class="o">=></span> <span class="k">fn</span><span class="p">(</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="nv">$mp</span><span class="p">,</span> <span class="nv">$pc</span><span class="p">)</span> <span class="o">=></span>
<span class="k">isset</span><span class="p">(</span><span class="nv">$p</span><span class="p">[</span><span class="nv">$pc</span><span class="p">])</span> <span class="o">&&</span> <span class="nv">$loop</span><span class="p">(</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="mf">...</span><span class="p">(</span><span class="nv">$p</span><span class="p">[</span><span class="nv">$pc</span><span class="p">](</span><span class="nv">$m</span><span class="p">,</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$b</span><span class="p">,</span> <span class="nv">$e</span><span class="p">,</span> <span class="nv">$mp</span><span class="p">,</span> <span class="nv">$pc</span><span class="p">)))</span>
<span class="p">)(</span><span class="nv">$mm</span><span class="p">(</span><span class="o">+!!</span><span class="p">[],</span> <span class="o">+</span><span class="p">(</span><span class="o">!</span><span class="p">[]</span><span class="mf">.</span><span class="o">!</span><span class="p">[])),</span> <span class="nv">$p</span><span class="p">,</span> <span class="nv">$id</span><span class="p">(</span><span class="err">$🤡</span><span class="p">),</span> <span class="nv">$id</span><span class="p">(</span><span class="err">$🎪</span><span class="p">),</span> <span class="o">+!!</span><span class="p">[],</span> <span class="o">+!!</span><span class="p">[]);</span>
<span class="err">$🐘</span><span class="p">([</span>
<span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span>
<span class="err">$🤡</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span>
<span class="err">$👈</span><span class="p">,</span> <span class="err">$👈</span><span class="p">,</span> <span class="err">$👈</span><span class="p">,</span> <span class="err">$👈</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span>
<span class="err">$🎪</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👎</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👈</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👉</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👈</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👈</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$👍</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👉</span><span class="p">,</span> <span class="err">$👎</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="err">$👈</span><span class="p">,</span> <span class="err">$📝</span><span class="p">,</span>
<span class="p">]);</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>この問題は、単に適切なバージョンの PHP で動かせばトークンが得られる。</p>
</div>
<section class="section-2">
<h3 id="" class="section-header">
解説
</h3>
<div class="section-body">
<section class="section-3">
<h4 id="" class="section-header">
絵文字
</h4>
<div class="section-body">
<div class="paragraph">
<p>まず目につくのは大量の絵文字だろう。 PHP
は識別子に使用できる文字の範囲が広く、絵文字も使うことができる。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
プログラム全体
</h4>
<div class="section-body">
<div class="paragraph">
<p>Brainf*ck のインタプリタとプログラムになっている。 Brainf*ck
とは、難解プログラミング言語のひとつであり、ここで説明するよりも
Wikipedia の該当ページを読んだ方がよい。</p>
</div>
<div class="paragraph">
<p><a href="https://ja.wikipedia.org/wiki/Brainfuck" class="bare">https://ja.wikipedia.org/wiki/Brainfuck</a></p>
</div>
<div class="paragraph">
<p>なお、brainf*ck プログラムを普通の書き方で書くと、次のようになる。</p>
</div>
<div class="literalblock">
<div class="content">
<pre>+ + + + + + + + + +
[
> + + +
> + + + + +
> + + + + + + + + + + + +
> + + + + + + + + + +
< < < < -
]
> + + + + + .
- - .
> - - - .
> - - - .
- - .
- .
< .
> > - - .
+ + + + + + + .
< - - - - .
< .
> + + .
> - .
< .</pre>
</div>
</div>
<div class="paragraph">
<p>実行結果はこちら: <a href="https://ideone.com/22VWmb" class="bare">https://ideone.com/22VWmb</a></p>
</div>
<div class="paragraph">
<p>それぞれの絵文字で表された関数が、各命令に対応している。</p>
</div>
<div class="ulist">
<ul>
<li>
<p><code>$👉</code>: <code>></code></p>
</li>
<li>
<p><code>$👈</code>: <code><</code></p>
</li>
<li>
<p><code>$👍</code>: <code>+</code></p>
</li>
<li>
<p><code>$👎</code>: <code>-</code></p>
</li>
<li>
<p><code>$📝</code>: <code>.</code></p>
</li>
<li>
<p><code>$🤡</code>: <code>[</code></p>
</li>
<li>
<p><code>$🎪</code>: <code>]</code></p>
</li>
</ul>
</div>
<div class="paragraph">
<p><code>,</code> (入力) に対応する関数はない
(このプログラムでは使わないので用意していない)。</p>
</div>
<div class="paragraph">
<p>なお、<code>$🐘</code> はいわゆる main 関数であり、プログラムの実行部分である。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
絵文字の選択
</h4>
<div class="section-body">
<div class="paragraph">
<p>おおよそ意味に合致するよう選んでいるが、<code>$🤡</code> と <code>$🎪</code>
は弊社デジタルサーカスにちなんでいる。 また、<code>$🐘</code> は PHP
のマスコットの象に由来する。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
strict_types
</h4>
<div class="section-body">
<div class="paragraph">
<p><code>declare</code> 文の <code>strict_types</code> に指定できるのは、<code>0</code> か <code>1</code>
の数値リテラルだが、 <code>0x0</code> や <code>0b1</code> のような値も受け付ける。 今回は、PHP
8.1 から追加された、<code>0O</code> または <code>0o</code> から始まる八進数リテラルを使った。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
URL
</h4>
<div class="section-body">
<div class="paragraph">
<p>ソースコードのライセンスを示したこの部分だが、</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"><span class="n">https</span><span class="o">://</span><span class="n">creativecommons</span><span class="mf">.</span><span class="n">org</span><span class="o">/</span><span class="n">publicdomain</span><span class="o">/</span><span class="n">zero</span><span class="o">/</span><span class="mf">1.0</span><span class="o">/</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>完全に合法な PHP のコードである。 <code>https:</code> 部分はラベル、<code>//</code>
以降は行コメントになっている。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
リテラルなしで数値を生成する
</h4>
<div class="section-body">
<div class="paragraph">
<p>ソースコード中に、ほとんど数値リテラルが書かれていないことにお気づきだろうか。
PHP では、型変換を利用することで任意の整数を作り出すことができる。</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"><span class="nb">assert</span><span class="p">(</span><span class="mi">0</span> <span class="o">===</span> <span class="o">+!!</span><span class="p">[]);</span>
<span class="nb">assert</span><span class="p">(</span><span class="mi">1</span> <span class="o">===</span> <span class="o">+!</span><span class="p">[]);</span>
<span class="nb">assert</span><span class="p">(</span><span class="mi">2</span> <span class="o">===</span> <span class="o">!</span><span class="p">[]</span><span class="o">+!</span><span class="p">[]);</span>
<span class="nb">assert</span><span class="p">(</span><span class="mi">3</span> <span class="o">===</span> <span class="o">!</span><span class="p">[]</span><span class="o">+!</span><span class="p">[]</span><span class="o">+!</span><span class="p">[]);</span>
<span class="nb">assert</span><span class="p">(</span><span class="mi">10</span> <span class="o">===</span> <span class="o">+</span><span class="p">(</span><span class="o">!</span><span class="p">[]</span><span class="mf">.</span><span class="o">+!!</span><span class="p">[]));</span></code></pre>
</div>
</div>
<div class="paragraph">
<p><code>[]</code> に <code>!</code> を適用すると <code>true</code> が返ってくる。それに <code>+</code>
を適用すると、<code>bool</code> から <code>int</code> ヘの型変換が走り、<code>1</code> が生成される。<code>10</code>
はさらにトリッキーだ。まず <code>1</code> と <code>0</code> を作り、<code>.</code> で文字列として結合する
(<code>'10'</code>)。これに <code>+</code> を適用すると、<code>string</code> から <code>int</code>
への型変換が走り、<code>10</code> が生まれる (コード量に頓着しないなら、<code>1</code> を 10
個足し合わせてももちろん 10 が作れる)。</p>
</div>
<div class="paragraph">
<p>また、<code>error_reporting</code> に指定しているのは <code>-1</code> である。 これは、<code>!</code>
によって文字列を <code>false</code> にし、<code>+</code> によって <code>false</code> を <code>0</code>
にし、さらにビット反転して <code>-1</code> にしている。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
<code>if</code> 文なしで条件分岐
</h4>
<div class="section-body">
<div class="paragraph">
<p>三項演算子ないし <code>match</code> 式を使うことで、<code>if</code>
を一切書かずに条件分岐ができる。 また、<code>&&</code> / <code>||</code> も使えることがある。
遅延評価が不要なケースでは、<code>[$t, $f][$cond]</code>
のような形で分岐することもできる。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
<code>while</code>、<code>for</code> 文なしでループ
</h4>
<div class="section-body">
<div class="paragraph">
<p>不動点コンビネータを使って無名再帰する
(詳しい説明は省略する。これらの単語で検索してほしい)。 ここでは、一般に
Z コンビネータとして知られるものを使った (<code>$z</code>)。</p>
</div>
<div class="paragraph">
<p>実際のところ、<code>$🤡</code> や <code>$🎪</code>、<code>$🐘</code> は、一度 Scheme (Lisp の一種)
で書いてから PHP に翻訳する形で記述した。</p>
</div>
<div class="paragraph">
<p>なお、PHP は末尾再帰の最適化をおこなわない (少なくとも今のところは)
ので、 あまりに長い brainf*ck
プログラムを書くとスタックオーバーフローする。</p>
</div>
</div>
</section>
</div>
</section>
</div>
</section>
<section class="section-1">
<h2 id="" class="section-header">
第2問 riddle.php
</h2>
<div class="section-body">
<div class="paragraph">
<p>ソースコードはこちら。実行には PHP 8.0 以上が必要なので注意。</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"><span class="o"><?</span><span class="n">php</span>
<span class="cd">/*********************************************************
* This program displays a PHPer token. *
* Guess 'N'. *
* *
* Hints: *
* - N itself has no special meaning, e.g., 42, 8128, *
* it is selected at random. *
* - Each element of $token represents a single letter. *
* - One letter consists of 5x5 cells. *
* - Remember, the output is a complete PHPer token. *
* *
* License: *
* https://creativecommons.org/publicdomain/zero/1.0/ *
*********************************************************/</span>
<span class="k">const</span> <span class="no">N</span> <span class="o">=</span> <span class="mi">0</span> <span class="cm">/* Change it to your answer. */</span><span class="p">;</span>
<span class="nb">assert</span><span class="p">(</span><span class="mi">0</span> <span class="o"><=</span> <span class="nc">N</span> <span class="o">&&</span> <span class="nc">N</span> <span class="o"><=</span> <span class="mb">0b11111_11111_11111_11111_11111</span><span class="p">);</span>
<span class="nv">$token</span> <span class="o">=</span> <span class="p">[</span>
<span class="mh">0x14B499C</span><span class="p">,</span>
<span class="mh">0x0BE34CC</span><span class="p">,</span> <span class="mh">0x01C9C69</span><span class="p">,</span>
<span class="mh">0x0ECA069</span><span class="p">,</span> <span class="mh">0x01C2449</span><span class="p">,</span> <span class="mh">0x0FDB166</span><span class="p">,</span> <span class="mh">0x01C9C69</span><span class="p">,</span>
<span class="mh">0x01C1C66</span><span class="p">,</span> <span class="mh">0x0FC1C47</span><span class="p">,</span> <span class="mh">0x01C1C66</span><span class="p">,</span>
<span class="mh">0x10C5858</span><span class="p">,</span> <span class="mh">0x1E4E3B8</span><span class="p">,</span> <span class="mh">0x1A2F2F8</span><span class="p">,</span>
<span class="p">];</span>
<span class="k">foreach</span> <span class="p">(</span><span class="nv">$token</span> <span class="k">as</span> <span class="nv">$x</span><span class="p">)</span> <span class="p">{</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nv">$x</span> <span class="o">^</span> <span class="nc">N</span><span class="p">;</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nb">sprintf</span><span class="p">(</span><span class="s1">'%025b'</span><span class="p">,</span> <span class="nv">$x</span><span class="p">);</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nb">str_replace</span><span class="p">(</span><span class="n">search</span><span class="o">:</span> <span class="p">[</span><span class="s1">'0'</span><span class="p">,</span> <span class="s1">'1'</span><span class="p">],</span> <span class="n">replace</span><span class="o">:</span> <span class="p">[</span><span class="s1">' '</span><span class="p">,</span> <span class="s1">'#'</span><span class="p">],</span> <span class="n">subject</span><span class="o">:</span> <span class="nv">$x</span><span class="p">);</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nb">implode</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">"</span><span class="p">,</span> <span class="nb">str_split</span><span class="p">(</span><span class="nv">$x</span><span class="p">,</span> <span class="n">length</span><span class="o">:</span> <span class="mi">5</span><span class="p">));</span>
<span class="k">echo</span> <span class="s2">"</span><span class="si">{</span><span class="nv">$x</span><span class="si">}</span><span class="se">\n\n</span><span class="s2">"</span><span class="p">;</span>
<span class="p">}</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>さて、この問題はさきほどのように単純に実行しただけでは、謎のブロックが表示されるだけでトークンは得られない。
トークンを得るためには、ソースコードを読み、定数 <code>N</code>
を特定する必要がある。</p>
</div>
<div class="paragraph">
<p>ここでは、私の想定解を解説する。</p>
</div>
<section class="section-2">
<h3 id="" class="section-header">
読解
</h3>
<div class="section-body">
<div class="paragraph">
<p>まずはソースコードを読んでいく。</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"><span class="nv">$token</span> <span class="o">=</span> <span class="p">[</span>
<span class="c1">// 略</span>
<span class="p">];</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>数値からなる <code>$token</code> があり、各要素をループしている。</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"> <span class="nv">$x</span> <span class="o">=</span> <span class="nv">$x</span> <span class="o">^</span> <span class="nc">N</span><span class="p">;</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>まずは排他的論理和 (xor) を取り、</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"> <span class="nv">$x</span> <span class="o">=</span> <span class="nb">sprintf</span><span class="p">(</span><span class="s1">'%025b'</span><span class="p">,</span> <span class="nv">$x</span><span class="p">);</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>二進数に変換して、</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"> <span class="nv">$x</span> <span class="o">=</span> <span class="nb">str_replace</span><span class="p">(</span><span class="n">search</span><span class="o">:</span> <span class="p">[</span><span class="s1">'0'</span><span class="p">,</span> <span class="s1">'1'</span><span class="p">],</span> <span class="n">replace</span><span class="o">:</span> <span class="p">[</span><span class="s1">' '</span><span class="p">,</span> <span class="s1">'#'</span><span class="p">],</span> <span class="n">subject</span><span class="o">:</span> <span class="nv">$x</span><span class="p">);</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>0 を空白に、1 を <code>#</code> にし、</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"> <span class="nv">$x</span> <span class="o">=</span> <span class="nb">implode</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">"</span><span class="p">,</span> <span class="nb">str_split</span><span class="p">(</span><span class="nv">$x</span><span class="p">,</span> <span class="n">length</span><span class="o">:</span> <span class="mi">5</span><span class="p">));</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>5文字ごとに区切ったあと、改行で結合している。</p>
</div>
</div>
</section>
<section class="section-2">
<h3 id="" class="section-header">
ヒント
</h3>
<div class="section-body">
<div class="paragraph">
<p>次に、ソースコードに書いてあるヒントを読んでいく。</p>
</div>
<div class="ulist">
<ul>
<li>
<p><code>N</code> それ自体は、42 や 8128
といったような特別な意味を持たず、ランダムに決められている</p>
</li>
<li>
<p><code>$token</code> の各要素は、1文字を表す</p>
</li>
<li>
<p>1文字は 5x5 のセルからなる</p>
</li>
<li>
<p>出力されるのは、完全な PHPer トークンである</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>ここで、PHPer トークンは必ず <code><mark></code> 記号から始まることを思いだすと、
<code>$token</code> の最初の数字 <code>0x14B499C</code> は、変換の結果 <code></mark></code>
になるのではないかと予想される (なお、このことは、リポジトリの README
ファイルに追加ヒントとして書かれている)。</p>
</div>
</div>
</section>
<section class="section-2">
<h3 id="" class="section-header">
解く
</h3>
<div class="section-body">
<div class="paragraph">
<p>ここまでわかれば、あと一歩で解ける。すなわち、<code>0x14B499C</code> が <code>#</code>
に変換されるような <code>N</code> を見つければよい。</p>
</div>
<div class="paragraph">
<p><code>N</code> は高々</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"><span class="nb">assert</span><span class="p">(</span><span class="mi">0</span> <span class="o"><=</span> <span class="nc">N</span> <span class="o">&&</span> <span class="nc">N</span> <span class="o"><=</span> <span class="mb">0b11111_11111_11111_11111_11111</span><span class="p">);</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>なのでブルートフォースしてもよいが、ここではブルートフォースしない方法を紹介する。</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"><span class="o"><?</span><span class="n">php</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="mh">0x14B499C</span><span class="p">;</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nv">$x</span> <span class="o">^</span> <span class="nc">N</span><span class="p">;</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nb">sprintf</span><span class="p">(</span><span class="s1">'%025b'</span><span class="p">,</span> <span class="nv">$x</span><span class="p">);</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nb">str_replace</span><span class="p">(</span><span class="n">search</span><span class="o">:</span> <span class="p">[</span><span class="s1">'0'</span><span class="p">,</span> <span class="s1">'1'</span><span class="p">],</span> <span class="n">replace</span><span class="o">:</span> <span class="p">[</span><span class="s1">' '</span><span class="p">,</span> <span class="s1">'#'</span><span class="p">],</span> <span class="n">subject</span><span class="o">:</span> <span class="nv">$x</span><span class="p">);</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nb">implode</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">"</span><span class="p">,</span> <span class="nb">str_split</span><span class="p">(</span><span class="nv">$x</span><span class="p">,</span> <span class="n">length</span><span class="o">:</span> <span class="mi">5</span><span class="p">));</span>
<span class="nb">assert</span><span class="p">(</span><span class="nv">$x</span> <span class="o">===</span>
<span class="s2">" # # </span><span class="se">\n</span><span class="s2">"</span> <span class="mf">.</span>
<span class="s2">"#####</span><span class="se">\n</span><span class="s2">"</span> <span class="mf">.</span>
<span class="s2">" # # </span><span class="se">\n</span><span class="s2">"</span> <span class="mf">.</span>
<span class="s2">"#####</span><span class="se">\n</span><span class="s2">"</span> <span class="mf">.</span>
<span class="s2">" # # "</span><span class="p">);</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>この一連の変換に対する逆変換を考えると、次のようになる。</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"><span class="o"><?</span><span class="n">php</span>
<span class="nv">$x</span> <span class="o">=</span>
<span class="s2">" # # </span><span class="se">\n</span><span class="s2">"</span> <span class="mf">.</span>
<span class="s2">"#####</span><span class="se">\n</span><span class="s2">"</span> <span class="mf">.</span>
<span class="s2">" # # </span><span class="se">\n</span><span class="s2">"</span> <span class="mf">.</span>
<span class="s2">"#####</span><span class="se">\n</span><span class="s2">"</span> <span class="mf">.</span>
<span class="s2">" # # "</span><span class="p">;</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nb">implode</span><span class="p">(</span><span class="s1">''</span><span class="p">,</span> <span class="nb">explode</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">"</span><span class="p">,</span> <span class="nv">$x</span><span class="p">));</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nb">str_replace</span><span class="p">(</span><span class="n">search</span><span class="o">:</span> <span class="p">[</span><span class="s1">' '</span><span class="p">,</span> <span class="s1">'#'</span><span class="p">],</span> <span class="n">replace</span><span class="o">:</span> <span class="p">[</span><span class="s1">'0'</span><span class="p">,</span> <span class="s1">'1'</span><span class="p">],</span> <span class="n">subject</span><span class="o">:</span> <span class="nv">$x</span><span class="p">);</span>
<span class="nv">$x</span> <span class="o">=</span> <span class="nb">bindec</span><span class="p">(</span><span class="nv">$x</span><span class="p">);</span>
<span class="nv">$n</span> <span class="o">=</span> <span class="nv">$x</span> <span class="o">^</span> <span class="mh">0x14B499C</span><span class="p">;</span>
<span class="k">echo</span> <span class="s2">"N = </span><span class="nv">$n</span><span class="se">\n</span><span class="s2">"</span><span class="p">;</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>これを実行すると、<code>N</code> が得られる。</p>
</div>
</div>
</section>
</div>
</section>
<section class="section-1">
<h2 id="" class="section-header">
第3問 toquine.php
</h2>
<div class="section-body">
<div class="paragraph">
<p>ソースコードはこちら。</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="php"><span class="o"><?</span><span class="n">php</span>
<span class="c1">// License: https://creativecommons.org/publicdomain/zero/1.0/</span>
<span class="c1">// This is a quine-like program to generate a PHPer token.</span>
<span class="c1">// Execute it like this: php toquine.php | php | php | php | ...</span>
<span class="nv">$s</span> <span class="o">=</span> <span class="sh"><<<'Q'
<?cuc
// Yvprafr: uggcf://perngvirpbzzbaf.bet/choyvpqbznva/mreb/1.0/
// Guvf vf n dhvar-yvxr cebtenz gb trarengr n CUCre gbxra.
// Rkrphgr vg yvxr guvf: cuc gbdhvar.cuc | cuc | cuc | cuc | ...
%f$f = %f;
$f = fge_ebg13($f); $kf = [
%f,
];
$g = ahyy.snyfr; sbe ($v = 0; $v <= vagqvi(__YVAR__-035,6); ++$v) vs (!vffrg($kf[$v])) oernx; ryfr
$g .= vzcybqr("\a", fge_fcyvg(fge_ercynpr(['0','1'], [' ','##'], fcevags(pue(37) . '025o', $kf[$v])), 012)) . "\a\a";
$jf = neenl_znc(sa($j) => vzcybqr(', ', $j), neenl_puhax(neenl_znc(sa($k) => fcevags('0k' . pue(37) . '07K', $k), $kf), 10));
cevags($f, $g, fge_ebg13("<<<'Q'\a{$f}\aQ"), vzcybqr(",\a", $jf));
Q;</span>
<span class="nv">$s</span> <span class="o">=</span> <span class="nb">str_rot13</span><span class="p">(</span><span class="nv">$s</span><span class="p">);</span> <span class="nv">$xs</span> <span class="o">=</span> <span class="p">[</span>
<span class="mh">0x0AFABEA</span><span class="p">,</span> <span class="mh">0x1F294A7</span><span class="p">,</span> <span class="mh">0x1F2109F</span><span class="p">,</span> <span class="mh">0x1F294A7</span><span class="p">,</span> <span class="mh">0x0002800</span><span class="p">,</span> <span class="mh">0x1F2109F</span><span class="p">,</span> <span class="mh">0x0117041</span><span class="p">,</span> <span class="mh">0x1F294A7</span><span class="p">,</span> <span class="mh">0x1FAD6B5</span><span class="p">,</span> <span class="mh">0x1F295B7</span><span class="p">,</span>
<span class="mh">0x010FC21</span><span class="p">,</span> <span class="mh">0x1FAD6B5</span><span class="p">,</span> <span class="mh">0x1151151</span><span class="p">,</span> <span class="mh">0x010FC21</span><span class="p">,</span> <span class="mh">0x1F294A7</span><span class="p">,</span> <span class="mh">0x1F295B7</span><span class="p">,</span> <span class="mh">0x1FAD6B5</span><span class="p">,</span> <span class="mh">0x1F294A7</span><span class="p">,</span> <span class="mh">0x1F295B7</span><span class="p">,</span> <span class="mh">0x1F8C63F</span><span class="p">,</span>
<span class="mh">0x1F8C631</span><span class="p">,</span> <span class="mh">0x1FAD6B5</span><span class="p">,</span> <span class="mh">0x17AD6BD</span><span class="p">,</span> <span class="mh">0x17AD6BD</span><span class="p">,</span> <span class="mh">0x1F8C63F</span><span class="p">,</span> <span class="mh">0x1F295B7</span><span class="p">,</span>
<span class="p">];</span>
<span class="nv">$t</span> <span class="o">=</span> <span class="kc">null</span><span class="mf">.</span><span class="kc">false</span><span class="p">;</span> <span class="k">for</span> <span class="p">(</span><span class="nv">$i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="nv">$i</span> <span class="o"><=</span> <span class="nb">intdiv</span><span class="p">(</span><span class="k">__LINE__</span><span class="o">-</span><span class="mo">035</span><span class="p">,</span><span class="mi">6</span><span class="p">);</span> <span class="o">++</span><span class="nv">$i</span><span class="p">)</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="k">isset</span><span class="p">(</span><span class="nv">$xs</span><span class="p">[</span><span class="nv">$i</span><span class="p">]))</span> <span class="k">break</span><span class="p">;</span> <span class="k">else</span>
<span class="nv">$t</span> <span class="mf">.</span><span class="o">=</span> <span class="nb">implode</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">"</span><span class="p">,</span> <span class="nb">str_split</span><span class="p">(</span><span class="nb">str_replace</span><span class="p">([</span><span class="s1">'0'</span><span class="p">,</span><span class="s1">'1'</span><span class="p">],</span> <span class="p">[</span><span class="s1">' '</span><span class="p">,</span><span class="s1">'##'</span><span class="p">],</span> <span class="nb">sprintf</span><span class="p">(</span><span class="nb">chr</span><span class="p">(</span><span class="mi">37</span><span class="p">)</span> <span class="mf">.</span> <span class="s1">'025b'</span><span class="p">,</span> <span class="nv">$xs</span><span class="p">[</span><span class="nv">$i</span><span class="p">])),</span> <span class="mo">012</span><span class="p">))</span> <span class="mf">.</span> <span class="s2">"</span><span class="se">\n\n</span><span class="s2">"</span><span class="p">;</span>
<span class="nv">$ws</span> <span class="o">=</span> <span class="nb">array_map</span><span class="p">(</span><span class="k">fn</span><span class="p">(</span><span class="nv">$w</span><span class="p">)</span> <span class="o">=></span> <span class="nb">implode</span><span class="p">(</span><span class="s1">', '</span><span class="p">,</span> <span class="nv">$w</span><span class="p">),</span> <span class="nb">array_chunk</span><span class="p">(</span><span class="nb">array_map</span><span class="p">(</span><span class="k">fn</span><span class="p">(</span><span class="nv">$x</span><span class="p">)</span> <span class="o">=></span> <span class="nb">sprintf</span><span class="p">(</span><span class="s1">'0x'</span> <span class="mf">.</span> <span class="nb">chr</span><span class="p">(</span><span class="mi">37</span><span class="p">)</span> <span class="mf">.</span> <span class="s1">'07X'</span><span class="p">,</span> <span class="nv">$x</span><span class="p">),</span> <span class="nv">$xs</span><span class="p">),</span> <span class="mi">10</span><span class="p">));</span>
<span class="nb">printf</span><span class="p">(</span><span class="nv">$s</span><span class="p">,</span> <span class="nv">$t</span><span class="p">,</span> <span class="nb">str_rot13</span><span class="p">(</span><span class="s2">"<<<'D'</span><span class="se">\n</span><span class="si">{</span><span class="nv">$s</span><span class="si">}</span><span class="se">\n</span><span class="s2">D"</span><span class="p">),</span> <span class="nb">implode</span><span class="p">(</span><span class="s2">",</span><span class="se">\n</span><span class="s2">"</span><span class="p">,</span> <span class="nv">$ws</span><span class="p">));</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>コメントにもあるとおり、次のようにして実行すれば答えがでてくる。</p>
</div>
<div id="source." class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="shell-session"><span class="gp">$</span><span class="w"> </span>php toquine.php | php | php | php | ...</code></pre>
</div>
</div>
<div class="paragraph">
<p>実際にはもう少しパイプで繋げなければならない。</p>
</div>
<section class="section-2">
<h3 id="" class="section-header">
解説
</h3>
<div class="section-body">
<section class="section-3">
<h4 id="" class="section-header">
プログラム全体
</h4>
<div class="section-body">
<div class="paragraph">
<p>コメントにもあるとおり、これは quine (風) のプログラムになっている。
Quine
とは、自分のソースコードをそっくりそのまま出力するようなプログラムのことである。</p>
</div>
<div class="paragraph">
<p>このプログラムは、実行すると自身とほとんど同じプログラムを出力する。
異なるのはトークンになっている部分のみである。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
トークン
</h4>
<div class="section-body">
<div class="paragraph">
<p><code>$xs</code> がトークンに対応している。変換のロジックは <code>riddle.php</code>
とほぼ同じなので省略する。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
状態保持
</h4>
<div class="section-body">
<div class="paragraph">
<p>トークンの何文字目まで出力したかを、ソースコードを変えずに (quine
なので) 覚えておく必要がある。
このプログラムでは、トークンが出力されるとソースコードがだんだんと長くなっていくのを利用して、<code><em>LINE</em></code>
から情報を取得している。</p>
</div>
</div>
</section>
<section class="section-3">
<h4 id="" class="section-header">
ROT 13
</h4>
<div class="section-body">
<div class="paragraph">
<p>Quine は、素朴に書くとプログラムの一部が 2回記述されてしまう。
これがあまり美しくないので、<code>toquine.php</code> では、ROT 13
変換を使って難読化した。</p>
</div>
<div class="paragraph">
<p>それにしてもなぜこんなものが標準ライブラリに……。</p>
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</section>
</div>
</section>
</div>
</section>
<section class="section-1">
<h2 id="" class="section-header">
おわりに
</h2>
<div class="section-body">
<div class="paragraph">
<p>解いていただいたみなさん、また、難易度調整につきあっていただいた社内のみなさん、ありがとうございました。</p>
</div>
<div class="paragraph">
<p>今回は直前に作りはじめたのもあり、3問だけかつ使い古されたネタばかりになってしまいましたが、
来年は 5問、より面白い問題を持っていきます。</p>
</div>
<div class="paragraph">
<p>実はもう作りはじめているので、どうか来年もありますように……。</p>
</div>
</div>
</section>
</div>
</article>
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