152 lines
13 KiB
HTML
152 lines
13 KiB
HTML
<!DOCTYPE html>
|
|
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
|
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<title>std::partition_point</title>
|
|
<link rel="stylesheet" href="ext.css" />
|
|
<link rel="stylesheet" href="site_modules.css" />
|
|
</head>
|
|
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_partition_point skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>partition_point</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-algorithm.html">algorithm</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dsc-header">
|
|
<td>
|
|
<div>定义于头文件 <code><a href="cpp-header-algorithm.html"><algorithm></a></code></div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody class="t-dcl-rev">
|
|
<tr class="t-dcl t-since-cxx11 t-until-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> ForwardIt, <span class="kw1">class</span> UnaryPredicate <span class="sy1">></span><br />
|
|
ForwardIt partition_point<span class="br0">(</span> ForwardIt first, ForwardIt last, UnaryPredicate p <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
|
|
<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> ForwardIt, <span class="kw1">class</span> UnaryPredicate <span class="sy1">></span><br />
|
|
<span class="kw4">constexpr</span> ForwardIt partition_point<span class="br0">(</span> ForwardIt first, ForwardIt last, UnaryPredicate p <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>检验（如同用 <span class="t-lc"><a href="cpp-algorithm-partition.html">std::partition</a></span> 的）划分范围 <code>[first, last)</code> ，并定位第一划分的结尾，即首个不满足 <code>p</code> 的元素，或若所有元素满足 <code>p</code> 则为 <code>last</code> 。</p>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>first, last</td>
|
|
<td>-</td>
|
|
<td>要检验的元素被划分范围</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>p</td>
|
|
<td>-</td>
|
|
<td>对于在范围起始找到的元素则返回 ​<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 的一元谓词。<br />
|
|
<p>对每个（可为 const 的） <code>VT</code> 类型参数 <code>v</code> ，其中 <code>VT</code> 是 <code>ForwardIt</code> 的值类型，表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="br0">(</span>v<span class="br0">)</span></span></span> 必须可转换为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> ，无关乎<a href="cpp-language-value_category.html">值类别</a>，而且必须不修改 <code>v</code> 。从而不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">VT<span class="sy3">&</span></span></span> 类型参数<span class="t-rev-inl t-since-cxx11"><span>，亦不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">VT</span></span> ，除非对 <code>VT</code> 而言移动等价于复制</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>。 ​</p>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-par-hitem">
|
|
<td colspan="3">类型要求</td>
|
|
</tr>
|
|
<tr class="t-par-req">
|
|
<td colspan="3">-
|
|
<div class="spacer"></div>
|
|
<code>ForwardIt</code> 必须满足<a href="cpp-named_req-ForwardIterator.html"><span style="font-style:italic">老式向前迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyForwardIterator)</span></a> 的要求。</td>
|
|
</tr>
|
|
<tr class="t-par-req">
|
|
<td colspan="3">-
|
|
<div class="spacer"></div>
|
|
<code>UnaryPredicate</code> 必须满足<a href="cpp-named_req-Predicate.html"><span style="font-style:italic">谓词</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Predicate)</span></a> 的要求。</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<p><code>[first, last)</code> 内第一划分结尾后的迭代器，或若所有元素满足 <code>p</code> 则为 <code>last</code> 。</p>
|
|
<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
|
|
<p>给定 <span class="t-c"><span class="mw-geshi cpp source-cpp">N <span class="sy1">=</span> <a href="cpp-iterator-distance.html"><span class="kw673">std::<span class="me2">distance</span></span></a><span class="br0">(</span>first, last<span class="br0">)</span></span></span> ，应用 <span class="texhtml" style="white-space: nowrap;">O(log N)</span> 次谓词 <code>p</code> 。</p>
|
|
<p>然而，对于非<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> ，迭代器自增次数为 <span class="texhtml" style="white-space: nowrap;">O(N)</span> 。</p>
|
|
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
|
<p>此算法是 <span class="t-lc"><a href="cpp-algorithm-lower_bound.html">std::lower_bound</a></span> 的更通用化的形式，能用 <code>std::partition_point</code> 以 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="sy3">&</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> e<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> e <span class="sy1"><</span> value<span class="sy4">;</span> <span class="br0">}</span></span></span> 为谓词表达它。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <algorithm></span>
|
|
<span class="co2">#include <array></span>
|
|
<span class="co2">#include <iostream></span>
|
|
<span class="co2">#include <iterator></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <span class="nu0">9</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="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">auto</span> is_even <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span><span class="br0">{</span> <span class="kw1">return</span> i <span class="sy2">%</span> <span class="nu0">2</span> <span class="sy1">==</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
|
|
<a href="cpp-algorithm-partition.html"><span class="kw1612">std::<span class="me2">partition</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>, is_even<span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">auto</span> p <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">partition_point</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>, is_even<span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Before partition:<span class="es1">\n</span> "</span><span class="sy4">;</span>
|
|
<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>, p, <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="kw1757">std::<span class="me2">cout</span></span></a>, <span class="st0">" "</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<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>After partition:<span class="es1">\n</span> "</span><span class="sy4">;</span>
|
|
<a href="cpp-algorithm-copy.html"><span class="kw1582">std::<span class="me2">copy</span></span></a><span class="br0">(</span>p, 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="kw1757">std::<span class="me2">cout</span></span></a>, <span class="st0">" "</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">Before partition:
|
|
8 2 6 4
|
|
After partition:
|
|
5 3 7 1 9</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-is_sorted.html"><span class="t-lines"><span>is_sorted</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>检查范围是否已按升序排列<br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-lower_bound.html"><span class="t-lines"><span>lower_bound</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回指向第一个<i>不小于</i>给定值的元素的迭代器<br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|