13 lines
4.8 KiB
HTML
13 lines
4.8 KiB
HTML
<!DOCTYPE html><html lang="zh-CN"><head><meta charset="utf-8"><meta name="X-UA-Compatible" content="IE=edge"><title> leetcode-409 · MarkDown</title><meta name="description" content="leetcode-409 - Ching"><meta name="viewport" content="width=device-width, initial-scale=1"><link rel="short icon" href="/favicon.png"><link rel="stylesheet" href="/css/apollo.css"><link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Source+Sans+Pro:400,600" type="text/css"><meta name="generator" content="Hexo 6.0.0"><link rel="alternate" href="/atom.xml" title="MarkDown" type="application/atom+xml">
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</head><body><header><a href="/" class="logo-link"><img src="/logo.png"></a><ul class="nav nav-list"><li class="nav-list-item"><a href="/" target="_self" class="nav-list-link">ALL</a></li><li class="nav-list-item"><a href="/categories/leetcode/" target="_self" class="nav-list-link">LEETCODE</a></li><li class="nav-list-item"><a href="/atom.xml" target="_self" class="nav-list-link">RSS</a></li></ul></header><section class="container"><div class="post"><article class="post-block"><h1 class="post-title">leetcode-409</h1><div class="post-meta"><div class="post-time">2020年3月25日</div></div><div class="post-content"><h3 id="409-最长回文串"><a href="#409-最长回文串" class="headerlink" title="409. 最长回文串"></a>409. 最长回文串</h3><p><a target="_blank" rel="noopener" href="https://leetcode-cn.com/problems/longest-palindrome/">题目</a></p>
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<p>一开始理解错题目了，以为是寻找字符串中的最长回文串，结果是构造。但是原理基本一样，由于回文中心对称，所以是由多个偶数个相同字母和至多一个奇数个相同字母组成。</p>
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<p>这样只要数给出的字符串中有几个偶数个相同字母和几个奇数个相同字母就可以了。奇数个相同字母可以减少一个当偶数个用，最后再加回去一个。</p>
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<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Solution</span>:</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">longestPalindrome</span>(<span class="params">self, s: <span class="built_in">str</span></span>) -> <span class="built_in">int</span>:</span></span><br><span class="line"> d = {}</span><br><span class="line"> <span class="keyword">for</span> l <span class="keyword">in</span> s:</span><br><span class="line"> <span class="keyword">if</span> <span class="keyword">not</span> l <span class="keyword">in</span> d:</span><br><span class="line"> d[l] = <span class="number">0</span></span><br><span class="line"> d[l] += <span class="number">1</span></span><br><span class="line"></span><br><span class="line"> i = <span class="number">0</span></span><br><span class="line"> odd = <span class="literal">False</span></span><br><span class="line"> <span class="keyword">for</span> k, v <span class="keyword">in</span> d.items():</span><br><span class="line"> <span class="keyword">if</span> v % <span class="number">2</span>:</span><br><span class="line"> i += (v-<span class="number">1</span>)</span><br><span class="line"> odd = <span class="literal">True</span></span><br><span class="line"> <span class="keyword">else</span>:</span><br><span class="line"> i += v</span><br><span class="line"> <span class="keyword">if</span> odd:</span><br><span class="line"> i += <span class="number">1</span></span><br><span class="line"> <span class="keyword">return</span> i</span><br><span class="line"></span><br><span class="line"><span class="comment">#40 ms 13.6 MB</span></span><br></pre></td></tr></table></figure>
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