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  <meta name="description" content="引自：《信息学奥赛之-数学一本通》 揍是这样： \[\operatorname{F}(n)&#x3D;\dfrac{\sqrt{5}}{5}\cdot\left[\left(1+\sqrt{5}\right)^n-\left(1-\sqrt{5}\right)^n\right]\] 代码揍这么简单： 123int ferbo(int n)&amp;#123;	return (sqrt(5)&#x2F;5)*(pow((1+s">
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          斐波那契数列-O(1)
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        <p>引自：《信息学奥赛之-数学一本通》 揍是这样： <span class="math display">\[\operatorname{F}(n)=\dfrac{\sqrt{5}}{5}\cdot\left[\left(1+\sqrt{5}\right)^n-\left(1-\sqrt{5}\right)^n\right]\]</span> 代码揍这么简单： <figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">ferbo</span><span class="params">(<span class="keyword">int</span> n)</span></span>&#123;</span><br><span class="line">	<span class="keyword">return</span> (<span class="built_in">sqrt</span>(<span class="number">5</span>)/<span class="number">5</span>)*(<span class="built_in">pow</span>((<span class="number">1</span>+<span class="built_in">sqrt</span>(<span class="number">5</span>))/<span class="number">2</span>,n)-<span class="built_in">pow</span>((<span class="number">1</span>-<span class="built_in">sqrt</span>(<span class="number">5</span>))/<span class="number">2</span>,n));</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure> 要是再加个快速幂就更棒了（够快了，懒得写）</p>

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