171 lines
18 KiB
HTML
171 lines
18 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<title>std::seed_seq::generate</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_random_seed_seq_generate skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::seed_seq::</span>generate</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-numeric.html">numeric</a>‎ | <a href="cpp-numeric-random.html">random</a>‎ | <a href="cpp-numeric-random-seed_seq.html">seed seq</a></span></div>
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<table class="t-dcl-begin">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> RandomIt <span class="sy1">></span><br />
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<span class="kw4">void</span> generate<span class="br0">(</span> RandomIt begin, RandomIt end <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>以基于最初提供于此 <code>seed_seq</code> 构造函数的无符号整数值 <code>i</code> ， <span class="texhtml" style="white-space: nowrap;">0 ≤ i < 2<span class="t-su">32<br /></span></span> 填充范围 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span>begin, end<span class="br0">)</span></span></span> 。产生的值分布在整个 32 位范围，即使初值有强偏差。</p>
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<p>使用下列算法（改编自<a rel="nofollow" class="external text" href="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html">松本真与西村拓士</a>发明的梅森缠绕器生成器，加以<a rel="nofollow" class="external text" href="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/M062821.pdf">斋藤睦夫于 2007</a> 的改进工作）。</p>
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<ul>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">begin <span class="sy1">==</span> end</span></span> 则不做任何事。否则，</li>
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</ul>
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<ul>
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<li>首先，设置输出范围的每个元素为值 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu12">0x8b8b8b8b</span></span></span> 。</li>
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</ul>
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<ul>
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<li>按照下列算法变换输出范围的元素：</li>
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</ul>
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<p>对于 <span class="t-c"><span class="mw-geshi cpp source-cpp">k <span class="sy1">=</span> <span class="nu0">0</span>,..., m<span class="sy2">-</span><span class="nu0">1</span></span></span><br /></p>
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<p>其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">m<span class="sy1">=</span>max<span class="br0">(</span>s<span class="sy2">+</span><span class="nu0">1</span>, n<span class="br0">)</span></span></span><br />
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而 <span class="t-c"><span class="mw-geshi cpp source-cpp">n<span class="sy1">=</span>end<span class="sy2">-</span>begin</span></span><br />
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而 <span class="t-c"><span class="mw-geshi cpp source-cpp">s<span class="sy1">=</span>v.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span></span></span><br />
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而 <span class="t-c"><span class="mw-geshi cpp source-cpp">v</span></span> 是保有最初为此 <code>seed_seq</code> 对象的构造函数所提供的值的私有容器，</p>
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<ol>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">begin<span class="br0">[</span>k<span class="sy2">+</span>p<span class="br0">]</span> <span class="sy2">+</span><span class="sy1">=</span> r1</span></span></li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">begin<span class="br0">[</span>k<span class="sy2">+</span>q<span class="br0">]</span> <span class="sy2">+</span><span class="sy1">=</span> r2</span></span></li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">begin<span class="br0">[</span>k<span class="br0">]</span> <span class="sy1">=</span> r2</span></span> ，</li>
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</ol>
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<p>其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="sy1">=</span><span class="br0">(</span>n<span class="sy2">-</span>t<span class="br0">)</span><span class="sy2">/</span><span class="nu0">2</span></span></span><br />
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而 <span class="t-c"><span class="mw-geshi cpp source-cpp">q<span class="sy1">=</span>p<span class="sy2">+</span>t</span></span><br />
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而 <span class="t-c"><span class="mw-geshi cpp source-cpp">t<span class="sy1">=</span><span class="br0">(</span>n <span class="sy1">>=</span> <span class="nu0">623</span><span class="br0">)</span> <span class="sy4">?</span> <span class="nu0">11</span> <span class="sy4">:</span> <span class="br0">(</span>n <span class="sy1">>=</span> <span class="nu0">68</span><span class="br0">)</span> <span class="sy4">?</span> <span class="nu0">7</span> <span class="sy4">:</span> <span class="br0">(</span>n <span class="sy1">>=</span> <span class="nu0">39</span><span class="br0">)</span> <span class="sy4">?</span> <span class="nu0">5</span> <span class="sy4">:</span> <span class="br0">(</span>n <span class="sy1">>=</span> <span class="nu0">7</span><span class="br0">)</span> <span class="sy4">?</span> <span class="nu0">3</span> <span class="sy4">:</span> <span class="br0">(</span>n <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">)</span> <span class="sy2">/</span> <span class="nu0">2</span></span></span><br />
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而 <span class="t-c"><span class="mw-geshi cpp source-cpp">r1<span class="sy1">=</span><span class="nu0">1664525</span> <span class="sy2">*</span> T<span class="br0">(</span>begin<span class="br0">[</span>k<span class="br0">]</span><span class="sy3">^</span>begin<span class="br0">[</span>k<span class="sy2">+</span>p<span class="br0">]</span><span class="sy3">^</span>begin<span class="br0">[</span>k−<span class="nu0">1</span><span class="br0">]</span><span class="br0">)</span></span></span><br />
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而 <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="br0">(</span>x<span class="br0">)</span> <span class="sy1">=</span> x <span class="sy3">^</span> <span class="br0">(</span>x <span class="sy1">>></span> <span class="nu0">27</span><span class="br0">)</span></span></span><br />
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而若 <span class="t-c"><span class="mw-geshi cpp source-cpp">k<span class="sy1">==</span><span class="nu0">0</span></span></span> 则 <span class="t-c"><span class="mw-geshi cpp source-cpp">r2<span class="sy1">=</span>r1<span class="sy2">+</span>s</span></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">0</span><span class="sy1"><</span>k<span class="sy1"><=</span>s</span></span> 则 <span class="t-c"><span class="mw-geshi cpp source-cpp">r2<span class="sy1">=</span>r1 <span class="sy2">+</span> k<span class="sy2">%</span>n <span class="sy2">+</span> v<span class="br0">[</span>k<span class="sy2">-</span><span class="nu0">1</span><span class="br0">]</span></span></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">k<span class="sy1">></span>s</span></span> 则 <span class="t-c"><span class="mw-geshi cpp source-cpp">r2<span class="sy1">=</span>r1 <span class="sy2">+</span> k<span class="sy2">%</span>n</span></span> 。</p>
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<p>对于 <span class="t-c"><span class="mw-geshi cpp source-cpp">k <span class="sy1">=</span> m,..., m<span class="sy2">+</span>n<span class="sy2">-</span><span class="nu0">1</span></span></span> ，</p>
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<ol>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">begin<span class="br0">[</span>k<span class="sy2">+</span>p<span class="br0">]</span> <span class="sy3">^</span><span class="sy1">=</span> r3</span></span></li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">begin<span class="br0">[</span>k<span class="sy2">+</span>q<span class="br0">]</span> <span class="sy3">^</span><span class="sy1">=</span> r4</span></span></li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">begin<span class="br0">[</span>k<span class="br0">]</span><span class="sy1">=</span>r4</span></span></li>
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</ol>
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<p>其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">r3 <span class="sy1">=</span> <span class="nu0">1566083941</span> <span class="sy2">*</span> T<span class="br0">(</span>begin<span class="br0">[</span>k<span class="br0">]</span><span class="sy2">+</span>begin<span class="br0">[</span>k<span class="sy2">+</span>p<span class="br0">]</span><span class="sy2">+</span>begin<span class="br0">[</span>k<span class="sy2">-</span><span class="nu0">1</span><span class="br0">]</span><span class="br0">)</span></span></span><br />
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而 <span class="t-c"><span class="mw-geshi cpp source-cpp">r4<span class="sy1">=</span>r3 <span class="sy2">-</span> k<span class="sy2">%</span>n</span></span></p>
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<p>其中，所有计算以 <span class="texhtml" style="white-space: nowrap;">modulo 2<span class="t-su">32<br /></span></span> 进行，并且以 <span class="texhtml" style="white-space: nowrap;">modulo n</span> 取输出范围的下标（ <span class="t-c"><span class="mw-geshi cpp source-cpp">begin<span class="br0">[</span>x<span class="br0">]</span></span></span> ）。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>begin, end</td>
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<td>-</td>
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<td>可变随机访问迭代器，其 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><></span><span class="sy4">::</span><span class="me2">value_type</span></span></span> 为适合存储 32 位值的无符号整数类型</td>
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</tr>
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<tr class="t-par-hitem">
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<td colspan="3">类型要求</td>
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</tr>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>RandomIt</code> 必须满足<a href="cpp-named_req-RandomAccessIterator.html"><span style="font-style:italic">老式随机访问迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyRandomAccessIterator)</span></a> 的要求。</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>无，写入结果到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span>begin, end<span class="br0">)</span></span></span> 范围。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>仅若 <code>begin</code> 和 <code>end</code> 上的操作抛出才抛异常。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <random></span>
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<span class="co2">#include <iostream></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-numeric-random-seed_seq.html"><span class="kw1501">std::<span class="me2">seed_seq</span></span></a> seq<span class="br0">(</span><span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><a href="cpp-types-integer.html"><span class="kw122">std::<span class="me2">uint32_t</span></span></a><span class="sy1">></span> seeds<span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span>
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seq.<span class="me1">generate</span><span class="br0">(</span>seeds.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, seeds.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 步骤 1 ：以 0x8b8b8b8b 填充</span>
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<span class="co1">// seeds = {2341178251, 2341178251, 2341178251, 2341178251, 2341178251,</span>
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<span class="co1">// 2341178251, 2341178251, 2341178251, 2341178251, 2341178251 }</span>
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<span class="co1">//</span>
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<span class="co1">// 步骤 2 ：</span>
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<span class="co1">// n = 10, s = 5, t = 3, p = 3, q = 6, m = 10</span>
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<span class="co1">//</span>
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<span class="co1">// 首次迭代， k = 0 ； r1 = 1371501266 ， r2 = 1371501271</span>
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<span class="co1">//</span>
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<span class="co1">// seeds = {1371501271, 2341178251, 2341178251, 3712679517, 2341178251,</span>
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<span class="co1">// 2341178251, 3712679522, 2341178251, 2341178251, 2341178251 }</span>
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<span class="co1">//</span>
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<span class="co1">// 从 k = 1 到 k = 5 迭代（ r2 = r1 + k%n + v[k-1] ）</span>
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<span class="co1">//</span>
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<span class="co1">// r1 = 2786190137, 3204727651, 4173325571, 1979226628, 401983366</span>
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<span class="co1">// r2 = 2786190139, 3204727655, 4173325577, 1979226636, 401983376</span>
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<span class="co1">//</span>
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<span class="co1">// seeds = {3350727907, 3188173515, 3204727655, 4173325577, 1979226636,</span>
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<span class="co1">// 401983376, 3591037797, 2811627722, 1652921976, 2219536532 } </span>
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<span class="co1">//</span>
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<span class="co1">// 从 k = 6 到 k = 9 迭代（ r2 = r1 + k%n ）</span>
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<span class="co1">//</span>
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<span class="co1">// r1 = 2718637909, 1378394210, 2297813071, 1608643617</span>
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<span class="co1">// r2 = 2718637915, 1378394217, 2297813079, 1608643626</span>
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<span class="co1">//</span>
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<span class="co1">// seeds = { 434154821, 1191019290, 3237041891, 1256752498, 4277039715,</span>
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<span class="co1">// 2010627002, 2718637915, 1378394217, 2297813079, 1608643626 } </span>
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<span class="co1">//</span>
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<span class="co1">// 步骤 3</span>
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<span class="co1">// 从 k = 10 到 k = 19 迭代，用 ^= 修改输出</span>
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<span class="co1">//</span>
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<span class="co1">// r1 = 1615303485, 3210438310, 893477041, 2884072672, 1918321961,</span>
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<span class="co1">// r2 = 1615303485, 3210438309, 893477039, 2884072669, 1918321957</span>
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<span class="co1">//</span>
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<span class="co1">// seeds = { 303093272, 3210438309, 893477039, 2884072669, 1918321957,</span>
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<span class="co1">// 1117182731, 1772877958, 2669970405, 3182737656, 4094066935 }</span>
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<span class="co1">//</span>
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<span class="co1">// r1 = 423054846, 46783064, 3904109085, 1534123446, 1495905687</span>
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<span class="co1">// r2 = 423054841, 46783058, 3904109078, 1534123438, 1495905678</span>
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<span class="co1">//</span>
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<span class="co1">// seeds = { 4204997637, 4246533866, 1856049002, 1129615051, 690460811,</span>
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<span class="co1">// 1075771511, 46783058, 3904109078, 1534123438, 1495905678 }</span>
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<span class="kw1">for</span><span class="br0">(</span><a href="cpp-types-integer.html"><span class="kw122">std::<span class="me2">uint32_t</span></span></a> n <span class="sy4">:</span> seeds<span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> n <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">4204997637
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4246533866
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1856049002
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1129615051
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690460811
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1075771511
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46783058
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3904109078
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1534123438
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1495905678</pre></div>
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</div>
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</div>
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</div>
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<div class="visualClear"></div>
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</div>
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</body>
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