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<div class="identifier-type">function template</div><div class="header"><algorithm></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">partial_sort</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">RandomAccessIterator</span><span class="o">></span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">partial_sort</span><span class="p">(</span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">middle</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">last</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++98</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">RandomAccessIterator</span><span class="o">></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">partial_sort</span><span class="p">(</span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">middle</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">last</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++20</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">RandomAccessIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Compare</span><span class="o">></span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">partial_sort</span><span class="p">(</span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">middle</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="n">Compare</span><span class="w"> </span><span class="n">comp</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++98</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">RandomAccessIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Compare</span><span class="o">></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">partial_sort</span><span class="p">(</span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">middle</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="n">Compare</span><span class="w"> </span><span class="n">comp</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++20</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">RandomAccessIterator</span><span class="o">></span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">partial_sort</span><span class="p">(</span><span class="n"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="o">&&</span><span class="w"> </span><span class="n">exec</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">middle</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">last</span><span class="p">);</span><span class="w"> </span><span class="c1">// (3) C++17</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">RandomAccessIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Compare</span><span class="o">></span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">partial_sort</span><span class="p">(</span><span class="n"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="o">&&</span><span class="w"> </span><span class="n">exec</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">middle</span><span class="p">,</span>
<span class="w"> </span><span class="n">RandomAccessIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="n">Compare</span><span class="w"> </span><span class="n">comp</span><span class="p">);</span><span class="w"> </span><span class="c1">// (4) C++17</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p><a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[first, last)</code>を部分的にソートし、先頭 <code>N</code> 個を順に並んだ状態にする。<code>N</code> は <code>middle - first</code> で決まる。</p>
<p>この関数は、「売り上げランキング トップ1位から10位まで」のように、全体ではなく最高順位から途中までの順位がわかればよい状況で、全体を並び替える<code><a href="sort.html">sort()</a></code>関数の代わりに使用できる。</p>
<p>なお、トップ10がどれかわかれば十分である（1位から10位までは順不同でよい）ような場合、<code><a href="nth_element.html">nth_element()</a></code>が使用できる。</p>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Constraints。関数であればオーバーロード解決に参加するための条件、それ以外であれば受け付ける型の条件">テンプレートパラメータ制約</a></h2>
<ul>
<li><code>RandomAccessIterator</code> は <code>ValueSwappable</code> の要件を満たしている必要がある。<code>*first</code> の型は <code>MoveConstructible</code> と <code>MoveAssignable</code> の要件を満たしていること</li>
</ul>
<h2>効果</h2>
<p><a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[first,last)</code>にある要素の中から、<code>middle - first</code> 個の要素をソート済みの状態で <code>[first,middle)</code> に配置する。残りの <code>[middle,last)</code> にある要素は<a class="cpprefjp-defined-word" data-desc="未規定の動作。事前の断りなく処理系によって異なる動作をする" href="../../implementation-compliance.html#dfn-unspecified-behavior">未規定</a>の順序に配置される。</p>
<h2><a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a></h2>
<p>なし</p>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Complexity。関数が使うアルゴリズムの空間計算量・時間計算量">計算量</a></h2>
<p>ほぼ <code>(last - first) * log(middle - first)</code> 回の比較を行う</p>
<h2>例</h2>
<p><div class="yata" id="5c4c85363e456e7dbdc44db01d40e8be7cc52db2"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../vector.html"><vector></a></span>
<span class="cp">#include <a href="../algorithm.html"><algorithm></a></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../vector/vector.html">std::vector</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">};</span>
<span class="w"> </span><span class="c1">// 先頭2要素を並んだ状態にする</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::partial_sort</span></span><span class="p">(</span><span class="n"><a href="../vector/vector/begin.html">v.begin()</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../vector/vector/begin.html">v.begin()</a></span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../vector/vector/end.html">v.end()</a></span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="for_each.html">std::for_each</a></span><span class="p">(</span><span class="n"><a href="../vector/vector/begin.html">v.begin()</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../vector/vector/end.html">v.end()</a></span><span class="p">,</span><span class="w"> </span><span class="p">[](</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="p">});</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p><pre><code>1
2
4
3
5
</code></pre></p>
<h2>関連項目</h2>
<ul>
<li><code><a href="ranges_partial_sort.html">ranges::partial_sort</a></code></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0879r0.html" target="_blank">P0879R0 Constexpr for <code>swap</code> and <code>swap</code> related functions</a></li>
</ul></div>
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