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Ching 482b55e66d feat(package.json): 重装依赖 
重装依赖

Signed-off-by: Ching <loooching@gmail.com>
2022-02-02 21:07:01 +08:00

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<!DOCTYPE html><html lang="zh-CN"><head><meta charset="utf-8"><meta name="X-UA-Compatible" content="IE=edge"><title> leetcode-121 · MarkDown</title><meta name="description" content="leetcode-121 - 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">
</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-121</h1><div class="post-meta"><div class="post-time">2020年3月17日</div></div><div class="post-content"><h3 id="121-买卖股票的最佳时机"><a href="#121-买卖股票的最佳时机" class="headerlink" title="121. 买卖股票的最佳时机"></a>121. 买卖股票的最佳时机</h3><p><a target="_blank" rel="noopener" href="https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock/">题目</a></p>
<span id="more"></span>
<p>原始答案：</p>
<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><span class="line">22</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">maxProfit</span>(<span class="params">self, prices</span>) -&gt; <span class="built_in">int</span>:</span></span><br><span class="line"> profit = <span class="number">0</span></span><br><span class="line"> <span class="keyword">if</span> <span class="keyword">not</span> prices:</span><br><span class="line"> <span class="keyword">return</span> profit</span><br><span class="line"> min_buyin = prices[<span class="number">0</span>]</span><br><span class="line"> max_sellout = prices[<span class="number">0</span>]</span><br><span class="line"> l = <span class="built_in">len</span>(prices)</span><br><span class="line"> i = <span class="number">0</span></span><br><span class="line"> <span class="keyword">for</span> buyin <span class="keyword">in</span> prices:</span><br><span class="line"> <span class="keyword">if</span> i == l:</span><br><span class="line"> <span class="keyword">return</span> profit</span><br><span class="line"> <span class="keyword">if</span> min_buyin &lt;= buyin:</span><br><span class="line"> max_sellout = <span class="built_in">max</span>(prices[i:])</span><br><span class="line"> p = max_sellout - min_buyin</span><br><span class="line"> <span class="keyword">if</span> p &gt; profit:</span><br><span class="line"> profit = p</span><br><span class="line"> <span class="keyword">if</span> buyin &lt; min_buyin:</span><br><span class="line"> min_buyin = buyin</span><br><span class="line"> i += <span class="number">1</span></span><br><span class="line"> <span class="keyword">return</span> profit</span><br><span class="line"><span class="comment">#1880 ms 14.4 MB</span></span><br></pre></td></tr></table></figure>
<p>主要思路是找到波谷，如果当前价格比前一天要低，则还是在去往波谷的路上；当价格比前一天高或相同时，则到达了一个波谷，计算波谷和之后的波峰的差，就是这一段的利润。将从头至尾过一次，就能找到所有波谷和其后波峰的差，返回最大的即可。但是这个明显地在重复max，时间复杂度是O(n^2)，看起来就很傻逼。</p>
<p>仔细想想，其实并不需要直接找出波谷后的波峰，只要在for loop时保持波谷为最低的那个，就能算出每一个后续与波谷的差，找最大差即可。改了下代码变成这样</p>
<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></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">maxProfit</span>(<span class="params">self, prices</span>) -&gt; <span class="built_in">int</span>:</span></span><br><span class="line"> profit = <span class="number">0</span></span><br><span class="line"> <span class="keyword">if</span> <span class="keyword">not</span> prices:</span><br><span class="line"> <span class="keyword">return</span> profit</span><br><span class="line"> min_buyin = prices[<span class="number">0</span>]</span><br><span class="line"> <span class="keyword">for</span> i <span class="keyword">in</span> <span class="built_in">range</span>(<span class="number">1</span>, <span class="built_in">len</span>(prices)):</span><br><span class="line"> min_buyin = <span class="built_in">min</span>(min_buyin, prices[i-<span class="number">1</span>])</span><br><span class="line"> profit = <span class="built_in">max</span>(prices[i] - min_buyin, profit)</span><br><span class="line"> <span class="keyword">return</span> profit</span><br><span class="line"> <span class="comment">#44 ms 14.4 MB</span></span><br></pre></td></tr></table></figure>
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