245 lines
20 KiB
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245 lines
20 KiB
HTML
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<title>std::random_shuffle, std::shuffle</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_random_shuffle 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::</span>random_shuffle, <span style="font-size:0.7em; line-height:130%">std::</span>shuffle</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-algorithm.html">algorithm</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<div>定义于头文件 <code><a href="cpp-header-algorithm.html"><algorithm></a></code></div>
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<td></td>
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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> random_shuffle<span class="br0">(</span> RandomIt first, RandomIt last <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark">(C++14 中弃用)</span><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></td>
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<tbody class="t-dcl-rev t-dcl-rev-num">
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<td rowspan="142">(2)</td>
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<td></td>
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<tr class="t-dcl t-until-cxx11">
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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="kw1">class</span> RandomFunc <span class="sy1">></span><br />
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<span class="kw4">void</span> random_shuffle<span class="br0">(</span> RandomIt first, RandomIt last, RandomFunc<span class="sy3">&</span> r <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-until-cxx11">(C++11 前)</span></td>
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<tr class="t-dcl t-since-cxx11 t-until-cxx17">
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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="kw1">class</span> RandomFunc <span class="sy1">></span><br />
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<span class="kw4">void</span> random_shuffle<span class="br0">(</span> RandomIt first, RandomIt last, RandomFunc<span class="sy3">&&</span> r <span class="br0">)</span><span class="sy4">;</span></span></div>
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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><br />
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<span class="t-mark">(C++14 中弃用)</span><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></td>
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<tbody>
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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="kw1">class</span> URBG <span class="sy1">></span><br />
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<span class="kw4">void</span> shuffle<span class="br0">(</span> RandomIt first, RandomIt last, URBG<span class="sy3">&&</span> g <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<td></td>
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<td></td>
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<p>重排序给定范围 <code>[first, last)</code> 中的元素，使得这些元素的每个排列拥有相等的出现概率。</p>
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<div class="t-li1"><span class="t-li">1)</span> 随机数生成器是实现定义的，但经常使用函数 <span class="t-lc"><a href="cpp-numeric-random-rand.html">std::rand</a></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 随机数生成器为函数对象 <code>r</code> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 随机数生成器为函数对象 <code>g</code> 。</div>
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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>first, last</td>
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<td>-</td>
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<td>要随机打乱的元素范围</td>
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</tr>
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<tr class="t-par">
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<td>r</td>
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<td>-</td>
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<td>函数对象。若以 <code>r(n)</code> 调用，则返回可转换为 <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>RandomIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span></span></span> 的在区间 [0,n) 中随机选取的值</td>
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<tr class="t-par">
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<td>g</td>
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<td>-</td>
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<td><a href="cpp-named_req-UniformRandomBitGenerator.html"><span style="font-style:italic">均匀随机位生成器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UniformRandomBitGenerator)</span></a> ，其结果类型可隐式转换为 <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>RandomIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span></span></span></td>
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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 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-ValueSwappable.html"><span style="font-style:italic">值可交换</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(ValueSwappable)</span></a> 和 <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 class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-remove_reference.html"><span class="kw607">std::<span class="me2">remove_reference_t</span></span></a><span class="sy1"><</span>URBG<span class="sy1">></span></span></span></code> 必须满足<a href="cpp-named_req-UniformRandomBitGenerator.html"><span style="font-style:italic">均匀随机位生成器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UniformRandomBitGenerator)</span></a> 的要求。</td>
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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）</p>
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<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
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<p>与 <code>first</code> 和 <code>last</code> 间的距离成线性。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>标准未钦定实现，故即使你用准确相同的 <code>RandomFunc</code> 或 <code>URBG</code> ，也可能通过不同的标准库实现得到不同结果。</p>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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<table class="eq-fun-cpp-table">
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<tr>
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<th>版本一</th>
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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="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> RandomIt <span class="sy1">></span>
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<span class="kw4">void</span> random_shuffle<span class="br0">(</span> RandomIt first, RandomIt last <span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>RandomIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span> i, n<span class="sy4">;</span>
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n <span class="sy1">=</span> last <span class="sy2">-</span> first<span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span>i <span class="sy1">=</span> n<span class="sy2">-</span><span class="nu0">1</span><span class="sy4">;</span> i <span class="sy1">></span> <span class="nu0">0</span><span class="sy4">;</span> <span class="sy2">--</span>i<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">using</span> <a href="cpp-algorithm-swap.html"><span class="kw1599">std::<span class="me2">swap</span></span></a><span class="sy4">;</span>
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swap<span class="br0">(</span>first<span class="br0">[</span>i<span class="br0">]</span>, first<span class="br0">[</span><a href="cpp-numeric-random-rand.html"><span class="kw1498">std::<span class="me2">rand</span></span></a><span class="br0">(</span><span class="br0">)</span> <span class="sy2">%</span> <span class="br0">(</span>i<span class="sy2">+</span><span class="nu0">1</span><span class="br0">)</span><span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// rand() % (i+1) 实际上不准确，因为生成的数对于多数 i 值不均匀分布。</span>
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<span class="co1">// 正确实现将实际上需要重新实现 C++11 std::uniform_distributtion ，</span>
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<span class="co1">// 这超出了此示例的范畴。</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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<tr>
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<th>版本二</th>
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</tr>
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<tr>
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<td>
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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="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> RandomIt, <span class="kw1">class</span> RandomFunc<span class="sy1">></span>
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<span class="kw4">void</span> random_shuffle<span class="br0">(</span>RandomIt first, RandomIt last, RandomFunc<span class="sy3">&&</span> r<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>RandomIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span> i, n<span class="sy4">;</span>
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n <span class="sy1">=</span> last <span class="sy2">-</span> first<span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span>i <span class="sy1">=</span> n<span class="sy2">-</span><span class="nu0">1</span><span class="sy4">;</span> i <span class="sy1">></span> <span class="nu0">0</span><span class="sy4">;</span> <span class="sy2">--</span>i<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">using</span> <a href="cpp-algorithm-swap.html"><span class="kw1599">std::<span class="me2">swap</span></span></a><span class="sy4">;</span>
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swap<span class="br0">(</span>first<span class="br0">[</span>i<span class="br0">]</span>, first<span class="br0">[</span>r<span class="br0">(</span>i<span class="sy2">+</span><span class="nu0">1</span><span class="br0">)</span><span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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<tr>
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<th>版本三</th>
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</tr>
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<tr>
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<td>
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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="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> RandomIt, <span class="kw1">class</span> URBG<span class="sy1">></span>
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<span class="kw4">void</span> shuffle<span class="br0">(</span>RandomIt first, RandomIt last, URBG<span class="sy3">&&</span> g<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">typedef</span> <span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>RandomIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span> diff_t<span class="sy4">;</span>
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<span class="kw1">typedef</span> <a href="cpp-numeric-random-uniform_int_distribution.html"><span class="kw1502">std::<span class="me2">uniform_int_distribution</span></span></a><span class="sy1"><</span>diff_t<span class="sy1">></span> distr_t<span class="sy4">;</span>
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<span class="kw1">typedef</span> <span class="kw1">typename</span> distr_t<span class="sy4">::</span><span class="me2">param_type</span> param_t<span class="sy4">;</span>
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distr_t D<span class="sy4">;</span>
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diff_t n <span class="sy1">=</span> last <span class="sy2">-</span> first<span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span>diff_t i <span class="sy1">=</span> n<span class="sy2">-</span><span class="nu0">1</span><span class="sy4">;</span> i <span class="sy1">></span> <span class="nu0">0</span><span class="sy4">;</span> <span class="sy2">--</span>i<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">using</span> <a href="cpp-algorithm-swap.html"><span class="kw1599">std::<span class="me2">swap</span></span></a><span class="sy4">;</span>
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swap<span class="br0">(</span>first<span class="br0">[</span>i<span class="br0">]</span>, first<span class="br0">[</span>D<span class="br0">(</span>g, param_t<span class="br0">(</span><span class="nu0">0</span>, i<span class="br0">)</span><span class="br0">)</span><span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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</table>
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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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<p>下列代码随机打乱整数 1..10 ：</p>
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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 <algorithm></span>
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<span class="co2">#include <iterator></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-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> v <span class="sy1">=</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="nu0">6</span>, <span class="nu0">7</span>, <span class="nu0">8</span>, <span class="nu0">9</span>, <span class="nu0">10</span><span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-numeric-random-random_device.html"><span class="kw1486">std::<span class="me2">random_device</span></span></a> rd<span class="sy4">;</span>
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<a href="cpp-numeric-random-mersenne_twister_engine.html"><span class="kw1489">std::<span class="me2">mt19937</span></span></a> g<span class="br0">(</span>rd<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">shuffle</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, g<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-algorithm-copy.html"><span class="kw1582">std::<span class="me2">copy</span></span></a><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <a href="cpp-iterator-ostream_iterator.html"><span class="kw670">std::<span class="me2">ostream_iterator</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">(</span><a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a>, <span class="st0">" "</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <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>可能的输出：</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">8 6 10 4 2 3 7 1 9 5</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-next_permutation.html"><span class="t-lines"><span>next_permutation</span></span></a></div>
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</div>
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</td>
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<td>产生某个元素范围的按字典顺序的下一个较大的排列<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-prev_permutation.html"><span class="t-lines"><span>prev_permutation</span></span></a></div>
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</div>
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</td>
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<td>产生某个元素范围的按字典顺序的下一个较小的排列<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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