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8.3 Top-K 问题
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8.3 Top-k 问题
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<a href="#1143" class="md-nav__link">
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11.4.3 插入排序优势
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11.4.3 插入排序的优势
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<li class="md-nav__item">
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<a href="#1143" class="md-nav__link">
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<span class="md-ellipsis">
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11.4.3 插入排序优势
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11.4.3 插入排序的优势
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<h2 id="1142">11.4.2 算法特性<a class="headerlink" href="#1142" title="Permanent link">¶</a></h2>
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<ul>
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<li><strong>时间复杂度 <span class="arithmatex">\(O(n^2)\)</span>、自适应排序</strong>:在最差情况下,每次插入操作分别需要循环 <span class="arithmatex">\(n - 1\)</span>、<span class="arithmatex">\(n-2\)</span>、<span class="arithmatex">\(\dots\)</span>、<span class="arithmatex">\(2\)</span>、<span class="arithmatex">\(1\)</span> 次,求和得到 <span class="arithmatex">\((n - 1) n / 2\)</span> ,因此时间复杂度为 <span class="arithmatex">\(O(n^2)\)</span> 。在遇到有序数据时,插入操作会提前终止。当输入数组完全有序时,插入排序达到最佳时间复杂度 <span class="arithmatex">\(O(n)\)</span> 。</li>
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<li><strong>空间复杂度 <span class="arithmatex">\(O(1)\)</span>、原地排序</strong>:指针 <span class="arithmatex">\(i\)</span> 和 <span class="arithmatex">\(j\)</span> 使用常数大小的额外空间。</li>
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<li><strong>时间复杂度为 <span class="arithmatex">\(O(n^2)\)</span>、自适应排序</strong>:在最差情况下,每次插入操作分别需要循环 <span class="arithmatex">\(n - 1\)</span>、<span class="arithmatex">\(n-2\)</span>、<span class="arithmatex">\(\dots\)</span>、<span class="arithmatex">\(2\)</span>、<span class="arithmatex">\(1\)</span> 次,求和得到 <span class="arithmatex">\((n - 1) n / 2\)</span> ,因此时间复杂度为 <span class="arithmatex">\(O(n^2)\)</span> 。在遇到有序数据时,插入操作会提前终止。当输入数组完全有序时,插入排序达到最佳时间复杂度 <span class="arithmatex">\(O(n)\)</span> 。</li>
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<li><strong>空间复杂度为 <span class="arithmatex">\(O(1)\)</span>、原地排序</strong>:指针 <span class="arithmatex">\(i\)</span> 和 <span class="arithmatex">\(j\)</span> 使用常数大小的额外空间。</li>
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<li><strong>稳定排序</strong>:在插入操作过程中,我们会将元素插入到相等元素的右侧,不会改变它们的顺序。</li>
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</ul>
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<h2 id="1143">11.4.3 插入排序优势<a class="headerlink" href="#1143" title="Permanent link">¶</a></h2>
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<h2 id="1143">11.4.3 插入排序的优势<a class="headerlink" href="#1143" title="Permanent link">¶</a></h2>
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<p>插入排序的时间复杂度为 <span class="arithmatex">\(O(n^2)\)</span> ,而我们即将学习的快速排序的时间复杂度为 <span class="arithmatex">\(O(n \log n)\)</span> 。尽管插入排序的时间复杂度更高,<strong>但在数据量较小的情况下,插入排序通常更快</strong>。</p>
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<p>这个结论与线性查找和二分查找的适用情况的结论类似。快速排序这类 <span class="arithmatex">\(O(n \log n)\)</span> 的算法属于基于分治策略的排序算法,往往包含更多单元计算操作。而在数据量较小时,<span class="arithmatex">\(n^2\)</span> 和 <span class="arithmatex">\(n \log n\)</span> 的数值比较接近,复杂度不占主导地位;每轮中的单元操作数量起到决定性作用。</p>
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<p>实际上,许多编程语言(例如 Java)的内置排序函数采用了插入排序,大致思路为:对于长数组,采用基于分治策略的排序算法,例如快速排序;对于短数组,直接使用插入排序。</p>
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