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3.1. &nbsp; 3.1. &nbsp; 数据与内存
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整数表示方式
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浮点数表示方式 *
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基本数据类型与数据结构的关系
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<h1>3.1. &nbsp; 数据与内存</h1>
<hr />
<h2 id="comments-true">comments: true<a class="headerlink" href="#comments-true" title="Permanent link">&para;</a></h2>
<h1 id="31-31">3.1. &nbsp; 3.1. &nbsp; 数据与内存<a class="headerlink" href="#31-31" title="Permanent link">&para;</a></h1>
<h2 id="311-311">3.1.1. &nbsp; 3.1.1. &nbsp; 基本数据类型<a class="headerlink" href="#311-311" title="Permanent link">&para;</a></h2>
2023-02-22 19:01:30 +08:00
<p>谈到计算机中的数据我们能够想到文本、图片、视频、语音、3D 模型等等,这些数据虽然组织形式不同,但都是由各种基本数据类型构成的。</p>
<p><strong>「基本数据类型」是 CPU 可以直接进行运算的类型,在算法中直接被使用</strong></p>
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<ul>
<li>「整数」根据不同的长度分为 byte, short, int, long ,根据算法需求选用,即在满足取值范围的情况下尽量减小内存空间占用;</li>
<li>「浮点数」代表小数,根据长度分为 float, double ,同样根据算法的实际需求选用;</li>
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<li>「字符」在计算机中是以字符集的形式保存的char 的值实际上是数字,代表字符集中的编号,计算机通过字符集查表来完成编号到字符的转换。占用空间通常为 2 bytes 或 1 byte </li>
<li>「布尔」代表逻辑中的“是”与“否”,其占用空间需根据编程语言确定,通常为 1 byte 或 1 bit </li>
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</ul>
<div class="center-table">
<table>
<thead>
<tr>
<th>类别</th>
<th>符号</th>
<th>占用空间</th>
<th>取值范围</th>
<th>默认值</th>
</tr>
</thead>
<tbody>
<tr>
<td>整数</td>
<td>byte</td>
<td>1 byte</td>
<td><span class="arithmatex">\(-2^7\)</span> ~ <span class="arithmatex">\(2^7 - 1\)</span> ( <span class="arithmatex">\(-128\)</span> ~ <span class="arithmatex">\(127\)</span> )</td>
<td><span class="arithmatex">\(0\)</span></td>
</tr>
<tr>
<td></td>
<td>short</td>
<td>2 bytes</td>
<td><span class="arithmatex">\(-2^{15}\)</span> ~ <span class="arithmatex">\(2^{15} - 1\)</span></td>
<td><span class="arithmatex">\(0\)</span></td>
</tr>
<tr>
<td></td>
<td><strong>int</strong></td>
<td>4 bytes</td>
<td><span class="arithmatex">\(-2^{31}\)</span> ~ <span class="arithmatex">\(2^{31} - 1\)</span></td>
<td><span class="arithmatex">\(0\)</span></td>
</tr>
<tr>
<td></td>
<td>long</td>
<td>8 bytes</td>
<td><span class="arithmatex">\(-2^{63}\)</span> ~ <span class="arithmatex">\(2^{63} - 1\)</span></td>
<td><span class="arithmatex">\(0\)</span></td>
</tr>
<tr>
<td>浮点数</td>
<td><strong>float</strong></td>
<td>4 bytes</td>
<td><span class="arithmatex">\(-3.4 \times 10^{38}\)</span> ~ <span class="arithmatex">\(3.4 \times 10^{38}\)</span></td>
<td><span class="arithmatex">\(0.0\)</span> f</td>
</tr>
<tr>
<td></td>
<td>double</td>
<td>8 bytes</td>
<td><span class="arithmatex">\(-1.7 \times 10^{308}\)</span> ~ <span class="arithmatex">\(1.7 \times 10^{308}\)</span></td>
<td><span class="arithmatex">\(0.0\)</span></td>
</tr>
<tr>
<td>字符</td>
<td><strong>char</strong></td>
<td>2 bytes / 1 byte</td>
<td><span class="arithmatex">\(0\)</span> ~ <span class="arithmatex">\(2^{16} - 1\)</span></td>
<td><span class="arithmatex">\(0\)</span></td>
</tr>
<tr>
<td>布尔</td>
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<td><strong>bool</strong></td>
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<td>1 byte / 1 bit</td>
<td><span class="arithmatex">\(\text{true}\)</span><span class="arithmatex">\(\text{false}\)</span></td>
<td><span class="arithmatex">\(\text{false}\)</span></td>
</tr>
</tbody>
</table>
</div>
<div class="admonition tip">
<p class="admonition-title">Tip</p>
<p>以上表格中,加粗项在「算法题」中最为常用。此表格无需硬背,大致理解即可,需要时可以通过查表来回忆。</p>
</div>
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<h3 id="_1">整数表示方式<a class="headerlink" href="#_1" title="Permanent link">&para;</a></h3>
<p>整数的取值范围取决于变量使用的内存长度,即字节(或比特)数。在计算机中, 1 字节 (byte) = 8 比特 (bit) 1 比特即 1 个二进制位。以 int 类型为例:</p>
<ol>
<li>整数类型 int 占用 4 bytes = 32 bits ,因此可以表示 <span class="arithmatex">\(2^{32}\)</span> 个不同的数字;</li>
<li>将最高位看作符号位,<span class="arithmatex">\(0\)</span> 代表正数,<span class="arithmatex">\(1\)</span> 代表负数,从而可以表示 <span class="arithmatex">\(2^{31}\)</span> 个正数和 <span class="arithmatex">\(2^{31}\)</span> 个负数;</li>
<li>当所有 bits 为 0 时代表数字 <span class="arithmatex">\(0\)</span> ,从零开始增大,可得最大正数为 <span class="arithmatex">\(2^{31} - 1\)</span> </li>
<li>剩余 <span class="arithmatex">\(2^{31}\)</span> 个数字全部用来表示负数,因此最小负数为 <span class="arithmatex">\(-2^{31}\)</span> ;具体细节涉及到到“源码、反码、补码”知识,有兴趣的同学可以查阅学习; </li>
</ol>
<p>其它整数类型 byte, short, long 取值范围的计算方法与 int 类似,在此不再赘述。</p>
<h3 id="_2">浮点数表示方式 *<a class="headerlink" href="#_2" title="Permanent link">&para;</a></h3>
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<div class="admonition note">
<p class="admonition-title">Note</p>
<p>在本书中,标题后的 <code>*</code> 符号代表选读章节,如果你觉得理解困难,建议先跳过,等学完必读章节后续再单独攻克。 </p>
</div>
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<p>细心的你可能会疑惑: int 和 float 长度相同,都是 4 bytes <strong>但为什么 float 的取值范围远大于 int</strong> ?按说 float 需要表示小数,取值范围应该变小才对。</p>
<p>其实,这是因为浮点数 float 采用了不同的表示方式。IEEE 754 标准规定32-bit 长度的 float 由以下部分构成:</p>
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<ul>
<li>符号位 <span class="arithmatex">\(\mathrm{S}\)</span> :占 1 bit </li>
<li>指数位 <span class="arithmatex">\(\mathrm{E}\)</span> :占 8 bits </li>
<li>分数位 <span class="arithmatex">\(\mathrm{N}\)</span> :占 24 bits ,其中 23 位显式存储;</li>
</ul>
<p>设 32-bit 二进制数的第 <span class="arithmatex">\(i\)</span> 位为 <span class="arithmatex">\(b_i\)</span> ,则 float 值的计算方法定义为</p>
<div class="arithmatex">\[
\text { val } = (-1)^{b_{31}} \times 2^{\left(b_{30} b_{29} \ldots b_{23}\right)_2-127} \times\left(1 . b_{22} b_{21} \ldots b_0\right)_2
\]</div>
<p>转化到十进制下的计算公式为</p>
<div class="arithmatex">\[
\text { val }=(-1)^{\mathrm{S}} \times 2^{\mathrm{E} -127} \times (1 + \mathrm{N})
\]</div>
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<p>其中各项的取值范围为</p>
<div class="arithmatex">\[
\begin{aligned}
\mathrm{S} \in &amp; \{ 0, 1\} , \quad \mathrm{E} \in \{ 1, 2, \dots, 254 \} \newline
(1 + \mathrm{N}) = &amp; (1 + \sum_{i=1}^{23} b_{23-i} 2^{-i}) \subset [1, 2 - 2^{-23}]
\end{aligned}
\]</div>
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<p><img alt="IEEE 754 标准下的 float 表示方式" src="../data_and_memory.assets/ieee_754_float.png" /></p>
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<p align="center"> Fig. IEEE 754 标准下的 float 表示方式 </p>
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<p align="center"> Fig. IEEE 754 标准下的 float 表示方式 </p>
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<p>以上图为例,<span class="arithmatex">\(\mathrm{S} = 0\)</span> <span class="arithmatex">\(\mathrm{E} = 124\)</span> <span class="arithmatex">\(\mathrm{N} = 2^{-2} + 2^{-3} = 0.375\)</span> ,易得</p>
<div class="arithmatex">\[
\text { val } = (-1)^0 \times 2^{124 - 127} \times (1 + 0.375) = 0.171875
\]</div>
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<p>现在我们可以回答开始的问题:<strong>float 的表示方式包含指数位,导致其取值范围远大于 int</strong> 。根据以上计算, float 可表示的最大正数为 <span class="arithmatex">\(2^{254 - 127} \times (2 - 2^{-23}) \approx 3.4 \times 10^{38}\)</span> ,切换符号位便可得到最小负数。</p>
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<p><strong>浮点数 float 虽然拓展了取值范围,但副作用是牺牲了精度</strong>。整数类型 int 将全部 32 位用于表示数字,数字是均匀分布的;而由于指数位的存在,浮点数 float 的数值越大,相邻两个数字之间的差值就会趋向越大。</p>
<p>进一步地,指数位 <span class="arithmatex">\(E = 0\)</span><span class="arithmatex">\(E = 255\)</span> 具有特殊含义,<strong>用于表示零、无穷大、<span class="arithmatex">\(\mathrm{NaN}\)</span></strong></p>
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<div class="center-table">
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<table>
<thead>
<tr>
<th>指数位 E</th>
<th>分数位 <span class="arithmatex">\(\mathrm{N} = 0\)</span></th>
<th>分数位 <span class="arithmatex">\(\mathrm{N} \ne 0\)</span></th>
<th>计算公式</th>
</tr>
</thead>
<tbody>
<tr>
<td><span class="arithmatex">\(0\)</span></td>
<td><span class="arithmatex">\(\pm 0\)</span></td>
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<td>次正规数</td>
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<td><span class="arithmatex">\((-1)^{\mathrm{S}} \times 2^{-126} \times (0.\mathrm{N})\)</span></td>
</tr>
<tr>
<td><span class="arithmatex">\(1, 2, \dots, 254\)</span></td>
<td>正规数</td>
<td>正规数</td>
<td><span class="arithmatex">\((-1)^{\mathrm{S}} \times 2^{(\mathrm{E} -127)} \times (1.\mathrm{N})\)</span></td>
</tr>
<tr>
<td><span class="arithmatex">\(255\)</span></td>
<td><span class="arithmatex">\(\pm \infty\)</span></td>
<td><span class="arithmatex">\(\mathrm{NaN}\)</span></td>
<td></td>
</tr>
</tbody>
</table>
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</div>
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<p>特别地,次正规数显著提升了小数精度:</p>
<ul>
<li>最小正正规数为 <span class="arithmatex">\(2^{-126} \approx 1.18 \times 10^{-38}\)</span> </li>
<li>最小正次正规数为 <span class="arithmatex">\(2^{-126} \times 2^{-23} \approx 1.4 \times 10^{-45}\)</span> </li>
</ul>
<p>双精度 double 也采用类似 float 的表示方法,在此不再赘述。</p>
<h3 id="_3">基本数据类型与数据结构的关系<a class="headerlink" href="#_3" title="Permanent link">&para;</a></h3>
<p>我们知道,<strong>数据结构是在计算机中组织与存储数据的方式</strong>,它的主语是“结构”,而不是“数据”。如果我们想要表示“一排数字”,自然想到使用「数组」数据结构。数组的存储方式可以表示数字的相邻关系、顺序关系,但至于其中存储的是整数 int ,还是小数 float ,或是字符 char <strong>则与所谓的数据的结构无关了</strong></p>
<p>换言之,基本数据类型提供了数据的“内容类型”,而数据结构提供数据的“组织方式”。</p>
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<div class="highlight"><pre><span></span><code><a id="__codelineno-0-1" name="__codelineno-0-1" href="#__codelineno-0-1"></a><span class="cm">/* 使用多种「基本数据类型」来初始化「数组」 */</span>
<a id="__codelineno-0-2" name="__codelineno-0-2" href="#__codelineno-0-2"></a><span class="kt">int</span><span class="o">[]</span><span class="w"> </span><span class="n">numbers</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">int</span><span class="o">[</span><span class="mi">5</span><span class="o">]</span><span class="p">;</span>
<a id="__codelineno-0-3" name="__codelineno-0-3" href="#__codelineno-0-3"></a><span class="kt">float</span><span class="o">[]</span><span class="w"> </span><span class="n">decimals</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">float</span><span class="o">[</span><span class="mi">5</span><span class="o">]</span><span class="p">;</span>
<a id="__codelineno-0-4" name="__codelineno-0-4" href="#__codelineno-0-4"></a><span class="kt">char</span><span class="o">[]</span><span class="w"> </span><span class="n">characters</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">char</span><span class="o">[</span><span class="mi">5</span><span class="o">]</span><span class="p">;</span>
<a id="__codelineno-0-5" name="__codelineno-0-5" href="#__codelineno-0-5"></a><span class="kt">boolean</span><span class="o">[]</span><span class="w"> </span><span class="n">booleans</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">boolean</span><span class="o">[</span><span class="mi">5</span><span class="o">]</span><span class="p">;</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><pre><span></span><code><a id="__codelineno-1-1" name="__codelineno-1-1" href="#__codelineno-1-1"></a><span class="cm">/* 使用多种「基本数据类型」来初始化「数组」 */</span>
<a id="__codelineno-1-2" name="__codelineno-1-2" href="#__codelineno-1-2"></a><span class="kt">int</span><span class="w"> </span><span class="n">numbers</span><span class="p">[</span><span class="mi">5</span><span class="p">];</span>
<a id="__codelineno-1-3" name="__codelineno-1-3" href="#__codelineno-1-3"></a><span class="kt">float</span><span class="w"> </span><span class="n">decimals</span><span class="p">[</span><span class="mi">5</span><span class="p">];</span>
<a id="__codelineno-1-4" name="__codelineno-1-4" href="#__codelineno-1-4"></a><span class="kt">char</span><span class="w"> </span><span class="n">characters</span><span class="p">[</span><span class="mi">5</span><span class="p">];</span>
<a id="__codelineno-1-5" name="__codelineno-1-5" href="#__codelineno-1-5"></a><span class="kt">bool</span><span class="w"> </span><span class="n">booleans</span><span class="p">[</span><span class="mi">5</span><span class="p">];</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><pre><span></span><code><a id="__codelineno-2-1" name="__codelineno-2-1" href="#__codelineno-2-1"></a><span class="sd">&quot;&quot;&quot; Python 的 list 可以自由存储各种基本数据类型和对象 &quot;&quot;&quot;</span>
<a id="__codelineno-2-2" name="__codelineno-2-2" href="#__codelineno-2-2"></a><span class="nb">list</span> <span class="o">=</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mf">0.0</span><span class="p">,</span> <span class="s1">&#39;a&#39;</span><span class="p">,</span> <span class="kc">False</span><span class="p">]</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><pre><span></span><code><a id="__codelineno-3-1" name="__codelineno-3-1" href="#__codelineno-3-1"></a><span class="c1">// 使用多种「基本数据类型」来初始化「数组」</span>
<a id="__codelineno-3-2" name="__codelineno-3-2" href="#__codelineno-3-2"></a><span class="kd">var</span><span class="w"> </span><span class="nx">numbers</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="kt">int</span><span class="p">{}</span>
<a id="__codelineno-3-3" name="__codelineno-3-3" href="#__codelineno-3-3"></a><span class="kd">var</span><span class="w"> </span><span class="nx">decimals</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="kt">float64</span><span class="p">{}</span>
<a id="__codelineno-3-4" name="__codelineno-3-4" href="#__codelineno-3-4"></a><span class="kd">var</span><span class="w"> </span><span class="nx">characters</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="kt">byte</span><span class="p">{}</span>
<a id="__codelineno-3-5" name="__codelineno-3-5" href="#__codelineno-3-5"></a><span class="kd">var</span><span class="w"> </span><span class="nx">booleans</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="kt">bool</span><span class="p">{}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><pre><span></span><code><a id="__codelineno-4-1" name="__codelineno-4-1" href="#__codelineno-4-1"></a><span class="cm">/* JavaScript 的数组可以自由存储各种基本数据类型和对象 */</span>
<a id="__codelineno-4-2" name="__codelineno-4-2" href="#__codelineno-4-2"></a><span class="kd">const</span><span class="w"> </span><span class="nx">array</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[</span><span class="mf">0</span><span class="p">,</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w"> </span><span class="s1">&#39;a&#39;</span><span class="p">,</span><span class="w"> </span><span class="kc">false</span><span class="p">];</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><pre><span></span><code><a id="__codelineno-5-1" name="__codelineno-5-1" href="#__codelineno-5-1"></a><span class="cm">/* 使用多种「基本数据类型」来初始化「数组」 */</span>
<a id="__codelineno-5-2" name="__codelineno-5-2" href="#__codelineno-5-2"></a><span class="kd">const</span><span class="w"> </span><span class="nx">numbers</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a id="__codelineno-5-3" name="__codelineno-5-3" href="#__codelineno-5-3"></a><span class="kd">const</span><span class="w"> </span><span class="nx">characters</span><span class="o">:</span><span class="w"> </span><span class="kt">string</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a id="__codelineno-5-4" name="__codelineno-5-4" href="#__codelineno-5-4"></a><span class="kd">const</span><span class="w"> </span><span class="nx">booleans</span><span class="o">:</span><span class="w"> </span><span class="kt">boolean</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><pre><span></span><code><a id="__codelineno-6-1" name="__codelineno-6-1" href="#__codelineno-6-1"></a><span class="cm">/* 使用多种「基本数据类型」来初始化「数组」 */</span>
<a id="__codelineno-6-2" name="__codelineno-6-2" href="#__codelineno-6-2"></a><span class="kt">int</span><span class="w"> </span><span class="n">numbers</span><span class="p">[</span><span class="mi">10</span><span class="p">];</span>
<a id="__codelineno-6-3" name="__codelineno-6-3" href="#__codelineno-6-3"></a><span class="kt">float</span><span class="w"> </span><span class="n">decimals</span><span class="p">[</span><span class="mi">10</span><span class="p">];</span>
<a id="__codelineno-6-4" name="__codelineno-6-4" href="#__codelineno-6-4"></a><span class="kt">char</span><span class="w"> </span><span class="n">characters</span><span class="p">[</span><span class="mi">10</span><span class="p">];</span>
<a id="__codelineno-6-5" name="__codelineno-6-5" href="#__codelineno-6-5"></a><span class="kt">bool</span><span class="w"> </span><span class="n">booleans</span><span class="p">[</span><span class="mi">10</span><span class="p">];</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><pre><span></span><code><a id="__codelineno-7-1" name="__codelineno-7-1" href="#__codelineno-7-1"></a><span class="cm">/* 使用多种「基本数据类型」来初始化「数组」 */</span>
<a id="__codelineno-7-2" name="__codelineno-7-2" href="#__codelineno-7-2"></a><span class="kt">int</span><span class="p">[]</span><span class="w"> </span><span class="n">numbers</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">int</span><span class="p">[</span><span class="m">5</span><span class="p">];</span>
<a id="__codelineno-7-3" name="__codelineno-7-3" href="#__codelineno-7-3"></a><span class="kt">float</span><span class="p">[]</span><span class="w"> </span><span class="n">decimals</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">float</span><span class="p">[</span><span class="m">5</span><span class="p">];</span>
<a id="__codelineno-7-4" name="__codelineno-7-4" href="#__codelineno-7-4"></a><span class="kt">char</span><span class="p">[]</span><span class="w"> </span><span class="n">characters</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">char</span><span class="p">[</span><span class="m">5</span><span class="p">];</span>
<a id="__codelineno-7-5" name="__codelineno-7-5" href="#__codelineno-7-5"></a><span class="kt">bool</span><span class="p">[]</span><span class="w"> </span><span class="n">booleans</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">bool</span><span class="p">[</span><span class="m">5</span><span class="p">];</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><pre><span></span><code><a id="__codelineno-8-1" name="__codelineno-8-1" href="#__codelineno-8-1"></a><span class="cm">/* 使用多种「基本数据类型」来初始化「数组」 */</span>
<a id="__codelineno-8-2" name="__codelineno-8-2" href="#__codelineno-8-2"></a><span class="kd">let</span> <span class="nv">numbers</span> <span class="p">=</span> <span class="nb">Array</span><span class="p">(</span><span class="n">repeating</span><span class="p">:</span> <span class="nb">Int</span><span class="p">(),</span> <span class="bp">count</span><span class="p">:</span> <span class="mi">5</span><span class="p">)</span>
<a id="__codelineno-8-3" name="__codelineno-8-3" href="#__codelineno-8-3"></a><span class="kd">let</span> <span class="nv">decimals</span> <span class="p">=</span> <span class="nb">Array</span><span class="p">(</span><span class="n">repeating</span><span class="p">:</span> <span class="nb">Double</span><span class="p">(),</span> <span class="bp">count</span><span class="p">:</span> <span class="mi">5</span><span class="p">)</span>
<a id="__codelineno-8-4" name="__codelineno-8-4" href="#__codelineno-8-4"></a><span class="kd">let</span> <span class="nv">characters</span> <span class="p">=</span> <span class="nb">Array</span><span class="p">(</span><span class="n">repeating</span><span class="p">:</span> <span class="nb">Character</span><span class="p">(</span><span class="s">&quot;a&quot;</span><span class="p">),</span> <span class="bp">count</span><span class="p">:</span> <span class="mi">5</span><span class="p">)</span>
<a id="__codelineno-8-5" name="__codelineno-8-5" href="#__codelineno-8-5"></a><span class="kd">let</span> <span class="nv">booleans</span> <span class="p">=</span> <span class="nb">Array</span><span class="p">(</span><span class="n">repeating</span><span class="p">:</span> <span class="nb">Bool</span><span class="p">(),</span> <span class="bp">count</span><span class="p">:</span> <span class="mi">5</span><span class="p">)</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><pre><span></span><code><a id="__codelineno-9-1" name="__codelineno-9-1" href="#__codelineno-9-1"></a>
</code></pre></div>
</div>
</div>
</div>
2023-03-07 01:16:02 +08:00
<h2 id="312-312">3.1.2. &nbsp; 3.1.2. &nbsp; 计算机内存<a class="headerlink" href="#312-312" title="Permanent link">&para;</a></h2>
2023-02-08 14:54:41 +08:00
<p>在计算机中,内存和硬盘是两种主要的存储硬件设备。「硬盘」主要用于长期存储数据,容量较大(通常可达到 TB 级别)、速度较慢。「内存」用于运行程序时暂存数据,速度较快,但容量较小(通常为 GB 级别)。</p>
<p><strong>算法运行中,相关数据都被存储在内存中</strong>。下图展示了一个计算机内存条,其中每个黑色方块都包含一块内存空间。我们可以将内存想象成一个巨大的 Excel 表格,其中每个单元格都可以存储 1 byte 的数据,在算法运行时,所有数据都被存储在这些单元格中。</p>
<p><strong>系统通过「内存地址 Memory Location」来访问目标内存位置的数据</strong>。计算机根据特定规则给表格中每个单元格编号,保证每块内存空间都有独立的内存地址。自此,程序便通过这些地址,访问内存中的数据。</p>
2023-02-26 18:18:03 +08:00
<p><img alt="内存条、内存空间、内存地址" src="../data_and_memory.assets/computer_memory_location.png" /></p>
2023-02-26 19:53:32 +08:00
<p align="center"> Fig. 内存条、内存空间、内存地址 </p>
2023-03-07 01:16:02 +08:00
<p align="center"> Fig. 内存条、内存空间、内存地址 </p>
2023-02-08 14:54:41 +08:00
<p><strong>内存资源是设计数据结构与算法的重要考虑因素</strong>。内存是所有程序的公共资源,当内存被某程序占用时,不能被其它程序同时使用。我们需要根据剩余内存资源的情况来设计算法。例如,若剩余内存空间有限,则要求算法占用的峰值内存不能超过系统剩余内存;若运行的程序很多、缺少大块连续的内存空间,则要求选取的数据结构必须能够存储在离散的内存空间内。</p>
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