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<meta name="description" content="在写24点纸牌算法时，有一个情况： 算法得到的表达式都是基本表达式，没有考虑运算符号之间的关系，导致冗余了括号。 例如：(3 * (1 * 2) * 4) 与 (3 * (1 * 2 * 4))其实是一样的表达式，应该进行优化。 优化的步骤分为： 分析表达式
统一乘法两边的大小顺序 …">
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<h1 class="entry-title"><a href="/blog/2013/08/20/use-ruby-reg-to-match-expression/">Ruby正则在表达式中的应用</a></h1>
<p class="meta">
<time datetime="2013-08-20T16:33:00+08:00" pubdate data-updated="true">Aug 20<span>th</span>, 2013</time>
| <a href="/blog/2013/08/20/use-ruby-reg-to-match-expression/#disqus_thread">Comments</a>
</p>
</header>
<div class="entry-content"><p>在写24点纸牌算法时，有一个情况：</p>
<blockquote><p>算法得到的表达式都是基本表达式，没有考虑运算符号之间的关系，导致冗余了括号。</p>
<p>例如：(3 * (1 * 2) * 4) 与 (3 * (1 * 2 * 4))其实是一样的表达式，应该进行优化。</p></blockquote>
<p>优化的步骤分为：</p>
<ul>
<li>分析表达式</li>
<li>统一乘法两边的大小顺序</li>
<li>移除乘除运算外面的括号</li>
</ul>
<p>分析一般表达式的构成，大致可以简化为 表达式E = (左括号left_bracket) + (表达式或数字E0) + (运算符operation) ＋ (表达式或数字E1) (右括号right_bracket)。
参考<a href="https://speakerdeck.com/luikore/more-than-regexp">超越正则的正则表达式</a>, 表达式的正则可以表示为：</p>
<figure class='code'><figcaption><span>表达式的正则</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
</pre></td><td class='code'><pre><code class='ruby'><span class='line'><span class="sr">/(?<expression>\(</span>
</span><span class='line'><span class="sr"> (?<left>(\g<expression>|\d*))</span>
</span><span class='line'><span class="sr"> (?<operate>[\+\-\*\/])</span>
</span><span class='line'><span class="sr"> (?<right>(\g<expression>|\d*))</span>
</span><span class='line'><span class="sr"> \))/</span>
</span></code></pre></td></tr></table></div></figure>
<p>这个正则可以匹配类似(1+2)、((1+2)*(3+4))这种表达式，如果想匹配没有括号包围的表达式如：1+2,应该再加上去除()的正则。</p>
<figure class='code'><figcaption><span>更完善的正则</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
</pre></td><td class='code'><pre><code class='ruby'><span class='line'><span class="sr">/(?<expression></span>
</span><span class='line'><span class="sr"> [\((?<left>(\g<expression>|\d*))</span>
</span><span class='line'><span class="sr"> (?<operate>[\+\-\*\/])</span>
</span><span class='line'><span class="sr"> (?<right>(\g<expression>|\d*))\) </span>
</span><span class='line'><span class="sr"> (?<left>(\g<expression>|\d*))</span>
</span><span class='line'><span class="sr"> (?<operate>[\+\-\*\/])</span>
</span><span class='line'><span class="sr"> (?<right>(\g<expression>|\d*))])/</span>
</span></code></pre></td></tr></table></div></figure>
<p>接下来，就是给乘法两边排序。不需要顾虑那么多，直接正则匹配到包含(E0*E1)的子表达式，进行排序替换。</p>
<figure class='code'><figcaption><span>排序替换</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
</pre></td><td class='code'><pre><code class='ruby'><span class='line'><span class="n">exp</span> <span class="o">=</span> <span class="s2">"(2*3)+5"</span>
</span><span class='line'><span class="k">if</span> <span class="sr">/(?<all_exp></span>
</span><span class='line'><span class="sr"> \((?<left_number>((?<expression_left>\(?(\d*)[\+\-\*\/](\d*|\g<expression_left>)\)?)|\d*))</span>
</span><span class='line'><span class="sr"> \*</span>
</span><span class='line'><span class="sr"> (?<right_number>((?<expression_right>\(?(\d*)[\+\-\*\/](\d*|\g<expression_right>)\)?)|\d*))\))/</span> <span class="o">=~</span> <span class="n">exp</span>
</span><span class='line'> <span class="n">left_number</span><span class="p">,</span> <span class="n">right_number</span> <span class="o">=</span> <span class="n">right_number</span><span class="p">,</span> <span class="n">left_number</span> <span class="k">if</span> <span class="n">left_number</span> <span class="o">=~</span> <span class="sr">/^\d*$/</span> <span class="o">&&</span> <span class="n">right_number</span> <span class="o">=~</span> <span class="sr">/^\d*$/</span> <span class="o">&&</span> <span class="n">left_number</span><span class="o">.</span><span class="n">to_i</span> <span class="o"><</span> <span class="n">right_number</span><span class="o">.</span><span class="n">to_i</span>
</span><span class='line'> <span class="n">s_exp</span> <span class="o">=</span> <span class="s2">"</span><span class="si">#{</span><span class="n">left_number</span><span class="si">}</span><span class="s2">*</span><span class="si">#{</span><span class="n">right_number</span><span class="si">}</span><span class="s2">"</span>
</span><span class='line'> <span class="n">exp</span><span class="o">.</span><span class="n">gsub!</span><span class="p">(</span><span class="n">all_exp</span><span class="p">,</span> <span class="n">s_exp</span><span class="p">)</span>
</span><span class='line'><span class="k">end</span>
</span><span class='line'><span class="nb">puts</span> <span class="n">exp</span> <span class="c1">#=> "3*2+5"</span>
</span></code></pre></td></tr></table></div></figure>
<p>最后的结果就成功的把乘法外面的括号移掉了，并按照左大右小的顺序排序。</p>
<p>除法的方式比乘法要简单一些,就不列举了。</p>
<p>还有一个类似(1+(2+3))以及((2+3)-2)这种也应该去括号，这样的话得到的表达式就能够去除大部分相同的表达式，从而实现最优。</p>
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<header>
<h1 class="entry-title"><a href="/blog/2013/08/09/resolve-uninstall-bundler-error/">卸载默认rake版本</a></h1>
<p class="meta">
<time datetime="2013-08-09T11:00:00+08:00" pubdate data-updated="true">Aug 9<span>th</span>, 2013</time>
| <a href="/blog/2013/08/09/resolve-uninstall-bundler-error/#disqus_thread">Comments</a>
</p>
</header>
<div class="entry-content"><p>重装系统和rvm后,ruby版本1.9.1,rake版本10.0.4.使用rake会爆出error:</p>
<figure class='code'><figcaption><span>rake error</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
</pre></td><td class='code'><pre><code class='ruby'><span class='line'><span class="ss">ERROR</span><span class="p">:</span> <span class="s1">'rake/rdoctask'</span> <span class="n">is</span> <span class="n">obsolete</span> <span class="ow">and</span> <span class="n">no</span> <span class="n">longer</span> <span class="n">supported</span><span class="o">.</span>
</span></code></pre></td></tr></table></div></figure>
<p>这里的原因在于rvm自动安装的rake版本过高,尝试安装0.9版本的,并卸载默认版本。</p>
<figure class='code'><figcaption><span>uninstall rake</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
</pre></td><td class='code'><pre><code class='ruby'><span class='line'><span class="n">gem</span> <span class="n">uninstall</span> <span class="n">rake</span> <span class="o">-</span><span class="n">v</span><span class="o">=</span><span class="mi">10</span><span class="o">.</span><span class="mi">0</span><span class="o">.</span><span class="mi">4</span>
</span></code></pre></td></tr></table></div></figure>
<p>还是有error爆出:</p>
<figure class='code'><figcaption><span>uninstall error</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class='ruby'><span class='line'><span class="ss">ERROR</span><span class="p">:</span> <span class="no">While</span> <span class="n">executing</span> <span class="n">gem</span> <span class="o">.</span><span class="n">.</span><span class="o">.</span> <span class="p">(</span><span class="ss">Gem</span><span class="p">:</span><span class="ss">:InstallError</span><span class="p">)</span>
</span><span class='line'> <span class="n">cannot</span> <span class="n">uninstall</span><span class="p">,</span> <span class="n">check</span> <span class="sb">`gem list -d`</span>
</span></code></pre></td></tr></table></div></figure>
<p>查看gem uninstall 帮助后，找到了解决方案:</p>
<figure class='code'><figcaption><span>help</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
<span class='line-number'>12</span>
</pre></td><td class='code'><pre><code class='ruby'><span class='line'><span class="n">gem</span> <span class="n">help</span> <span class="n">uninstall</span>
</span><span class='line'><span class="o">>></span><span class="ss">Defaults</span><span class="p">:</span>
</span><span class='line'><span class="o">>></span> <span class="o">--</span><span class="n">version</span> <span class="s1">'>= 0'</span> <span class="o">--</span><span class="n">no</span><span class="o">-</span><span class="n">force</span> <span class="o">--</span><span class="n">install</span><span class="o">-</span><span class="n">dir</span> <span class="sr">/Users/xxx</span><span class="o">/.</span><span class="n">rvm</span><span class="o">/</span><span class="n">gems</span><span class="o">/</span><span class="n">ruby</span><span class="o">-</span><span class="mi">1</span><span class="o">.</span><span class="mi">9</span><span class="o">.</span><span class="mi">1</span><span class="o">-</span><span class="n">p431</span>
</span><span class='line'><span class="n">gem</span> <span class="n">list</span> <span class="n">rake</span> <span class="o">-</span><span class="n">d</span>
</span><span class='line'>
</span><span class='line'><span class="n">rake</span> <span class="p">(</span><span class="mi">10</span><span class="o">.</span><span class="mi">0</span><span class="o">.</span><span class="mi">4</span><span class="p">,</span> <span class="mi">0</span><span class="o">.</span><span class="mi">9</span><span class="o">.</span><span class="mi">2</span><span class="o">.</span><span class="mi">2</span><span class="p">)</span>
</span><span class='line'> <span class="ss">Author</span><span class="p">:</span> <span class="no">Jim</span> <span class="no">Weirich</span>
</span><span class='line'> <span class="ss">Rubyforge</span><span class="p">:</span> <span class="ss">http</span><span class="p">:</span><span class="sr">//</span><span class="n">rubyforge</span><span class="o">.</span><span class="n">org</span><span class="o">/</span><span class="n">projects</span><span class="o">/</span><span class="n">rake</span>
</span><span class='line'> <span class="ss">Homepage</span><span class="p">:</span> <span class="ss">http</span><span class="p">:</span><span class="sr">//</span><span class="n">rake</span><span class="o">.</span><span class="n">rubyforge</span><span class="o">.</span><span class="n">org</span>
</span><span class='line'> <span class="ss">License</span><span class="p">:</span> <span class="no">MIT</span>
</span><span class='line'> <span class="no">Installed</span> <span class="n">at</span> <span class="p">(</span><span class="mi">10</span><span class="o">.</span><span class="mi">0</span><span class="o">.</span><span class="mi">4</span><span class="p">):</span> <span class="sr">/Users/xxx</span><span class="o">/.</span><span class="n">rvm</span><span class="o">/</span><span class="n">gems</span><span class="o">/</span><span class="n">ruby</span><span class="o">-</span><span class="mi">1</span><span class="o">.</span><span class="mi">9</span><span class="o">.</span><span class="mi">1</span><span class="o">-</span><span class="n">p431</span><span class="vi">@global</span>
</span><span class='line'> <span class="p">(</span><span class="mi">0</span><span class="o">.</span><span class="mi">9</span><span class="o">.</span><span class="mi">2</span><span class="o">.</span><span class="mi">2</span><span class="p">):</span> <span class="sr">/Users/xxx</span><span class="o">/.</span><span class="n">rvm</span><span class="o">/</span><span class="n">gems</span><span class="o">/</span><span class="n">ruby</span><span class="o">-</span><span class="mi">1</span><span class="o">.</span><span class="mi">9</span><span class="o">.</span><span class="mi">1</span><span class="o">-</span><span class="n">p431</span>
</span></code></pre></td></tr></table></div></figure>
<p>可以看到rake安装在两个不同的目录下，但默认uninstall的路径是在没有global的gem里。所以要卸载默认rake需要带上参数-i /Users/xxx/.rvm/gems/ruby-1.9.1-p431@global或者–install-dir /Users/xxx/.rvm/gems/ruby-1.9.1-p431@global</p>
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