217 lines
18 KiB
HTML
217 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::prev_permutation</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_prev_permutation 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>prev_permutation</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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<td></td>
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<td rowspan="142">(1)</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> BidirIt <span class="sy1">></span><br />
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<span class="kw4">bool</span> prev_permutation<span class="br0">(</span> BidirIt first, BidirIt last<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-until-cxx20">(C++20 前)</span></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> BidirIt <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> prev_permutation<span class="br0">(</span> BidirIt first, BidirIt last<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<td rowspan="142">(2)</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> BidirIt, <span class="kw1">class</span> Compare <span class="sy1">></span><br />
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<span class="kw4">bool</span> prev_permutation<span class="br0">(</span> BidirIt first, BidirIt last, Compare comp<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-until-cxx20">(C++20 前)</span></td>
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<tr class="t-dcl t-since-cxx20">
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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> BidirIt, <span class="kw1">class</span> Compare <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> prev_permutation<span class="br0">(</span> BidirIt first, BidirIt last, Compare comp<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>变换范围 <code>[first, last)</code> 为来自于相对于 <code>operator<</code> 或 <code>comp</code> 的字典序的所有排列集合的上个排列。若这种排列存在则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则变换范围为末排列（如同用 <code>std::sort(first, last); std::reverse(first, last);</code> ）并返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</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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<td>first, last</td>
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<td>-</td>
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<td>要重排的元素范围</td>
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<tr class="t-par">
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<td>comp</td>
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<td>-</td>
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<td>比较函数对象（即满足<a href="cpp-named_req-Compare.html"><span style="font-style:italic">比较</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Compare)</span></a> 要求的对象），若首个参数<i>小于</i>第二个，则返回 ​<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。<br />
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<p>比较函数的签名应等价于如下：</p>
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<p><span class="t-cc"><span class="mw-geshi cpp source-cpp"> <span class="kw4">bool</span> cmp<span class="br0">(</span><span class="kw4">const</span> Type1 <span class="sy3">&</span>a, <span class="kw4">const</span> Type2 <span class="sy3">&</span>b<span class="br0">)</span><span class="sy4">;</span></span></span></p>
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<p>虽然签名不必有 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="sy3">&</span></span></span> ，函数也不能修改传递给它的对象，而且必须接受（可为 const 的）类型 <code>Type1</code> 与 <code>Type2</code> 的值，无关乎<a href="cpp-language-value_category.html">值类别</a>（从而不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1 <span class="sy3">&</span></span></span> <span class="t-rev-inl t-since-cxx11"><span>，亦不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1</span></span> ，除非 <code>Type1</code> 的移动等价于复制</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>）。<br />
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类型 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type2</span></span> 必须使得 <span class="t-c"><span class="mw-geshi cpp source-cpp">BidirIt</span></span> 类型的对象能在解引用后隐式转换到这两个类型。 ​</p>
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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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<td colspan="3">-
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<div class="spacer"></div>
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<code>BidirIt</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-BidirectionalIterator.html"><span style="font-style:italic">老式双向迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyBidirectionalIterator)</span></a> 的要求。</td>
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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>若新排列按字典序前趋旧排列则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。若抵达首个排列并重置范围为最末排列则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</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>任何从迭代器操作或元素交换抛出的异常。</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>至多 <code>(last-first)/2</code> 次交换。</p>
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<p>典型实现在排列的整个序列上，平均每次调用使用约 3 次比较和 1.5 次交换。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>实现（例如 <a rel="nofollow" class="external text" href="https://github.com/microsoft/STL/blob/main/stl/src/vector_algorithms.cpp">MSVC STL</a> ）可能在迭代器类型满足<a href="cpp-named_req-ContiguousIterator.html"><span style="font-style:italic">老式连续迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyContiguousIterator)</span></a> ，并且交换其值类型不调用非平凡的特殊成员函数或 <a href="cpp-language-adl.html">ADL</a> 所找到的 <code>swap</code> 时启用向量化。</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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<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> BidirIt<span class="sy1">></span>
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<span class="kw4">bool</span> prev_permutation<span class="br0">(</span>BidirIt first, BidirIt last<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>first <span class="sy1">==</span> last<span class="br0">)</span> <span class="kw1">return</span> <span class="kw2">false</span><span class="sy4">;</span>
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BidirIt i <span class="sy1">=</span> last<span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>first <span class="sy1">==</span> <span class="sy2">--</span>i<span class="br0">)</span> <span class="kw1">return</span> <span class="kw2">false</span><span class="sy4">;</span>
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<span class="kw1">while</span> <span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span> <span class="br0">{</span>
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BidirIt i1, i2<span class="sy4">;</span>
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i1 <span class="sy1">=</span> i<span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span><span class="sy2">*</span>i1 <span class="sy1"><</span> <span class="sy2">*--</span>i<span class="br0">)</span> <span class="br0">{</span>
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i2 <span class="sy1">=</span> last<span class="sy4">;</span>
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<span class="kw1">while</span> <span class="br0">(</span><span class="sy3">!</span><span class="br0">(</span><span class="sy2">*--</span>i2 <span class="sy1"><</span> <span class="sy2">*</span>i<span class="br0">)</span><span class="br0">)</span>
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<span class="sy4">;</span>
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<a href="cpp-algorithm-iter_swap.html"><span class="kw1601">std::<span class="me2">iter_swap</span></span></a><span class="br0">(</span>i, i2<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-algorithm-reverse.html"><span class="kw1602">std::<span class="me2">reverse</span></span></a><span class="br0">(</span>i1, last<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> <span class="kw2">true</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">if</span> <span class="br0">(</span>i <span class="sy1">==</span> first<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-algorithm-reverse.html"><span class="kw1602">std::<span class="me2">reverse</span></span></a><span class="br0">(</span>first, last<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> <span class="kw2">false</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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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>下列代码以逆序打印字符串 "abc" 的所有六个排列</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 <algorithm></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <functional></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-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> s<span class="sy1">=</span><span class="st0">"abc"</span><span class="sy4">;</span>
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<a href="cpp-algorithm-sort.html"><span class="kw1618">std::<span class="me2">sort</span></span></a><span class="br0">(</span>s.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, s.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <a href="cpp-utility-functional-greater.html"><span class="kw1037">std::<span class="me2">greater</span></span></a><span class="sy1"><</span><span class="kw4">char</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">do</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> s <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">while</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">prev_permutation</span><span class="br0">(</span>s.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, s.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</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="kw1757">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>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">cba cab bca bac acb abc</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-is_permutation.html"><span class="t-lines"><span>is_permutation</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>判断一个序列是否为另一个序列的排列<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-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-ranges-prev_permutation.html"><span class="t-lines"><span>ranges::prev_permutation</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></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序下一个较小的排列<br />
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<span class="t-mark">(niebloid)</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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</body>
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