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11 lines
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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-number-of-islands · MarkDown</title><meta name="description" content="leetcode-number-of-islands - 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-number-of-islands</h1><div class="post-meta"><div class="post-time">2020年4月21日</div></div><div class="post-content"><h3 id="200-岛屿数量"><a href="#200-岛屿数量" class="headerlink" title="200. 岛屿数量"></a>200. 岛屿数量</h3><p><a target="_blank" rel="noopener" href="https://leetcode-cn.com/problems/number-of-islands/">题目</a></p>
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<p>这种矩阵题现在第一反应就是用<a href="(https://zh.wikipedia.org/zh-cn/%E5%B9%BF%E5%BA%A6%E4%BC%98%E5%85%88%E6%90%9C%E7%B4%A2)">广度优先搜索</a>做，类似之前算和0之间的距离那题。遍历矩阵，遇到 1 就将 1 改成 0，然后广度优先搜索找出 1 相邻的所有 1，这就是一个岛屿，以此类推。</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="keyword">import</span> collections</span><br><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">numIslands</span>(<span class="params">self, grid</span>) -> <span class="built_in">int</span>:</span></span><br><span class="line"> rows = <span class="built_in">len</span>(grid)</span><br><span class="line"> <span class="keyword">if</span> <span class="keyword">not</span> rows:</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span></span><br><span class="line"> cols = <span class="built_in">len</span>(grid[<span class="number">0</span>])</span><br><span class="line"> islands = <span class="number">0</span></span><br><span class="line"> <span class="keyword">for</span> r <span class="keyword">in</span> <span class="built_in">range</span>(rows):</span><br><span class="line"> <span class="keyword">for</span> l <span class="keyword">in</span> <span class="built_in">range</span>(cols):</span><br><span class="line"> <span class="keyword">if</span> grid[r][l] == <span class="string">'1'</span>:</span><br><span class="line"> islands += <span class="number">1</span></span><br><span class="line"> grid[r][l] = <span class="string">'0'</span></span><br><span class="line"> neighbors = collections.deque([(r, l)])</span><br><span class="line"> <span class="keyword">while</span> neighbors:</span><br><span class="line"> x, y = neighbors.popleft()</span><br><span class="line"> <span class="keyword">for</span> x_, y_ <span class="keyword">in</span> [[x-<span class="number">1</span>, y], [x+<span class="number">1</span>, y], [x, y-<span class="number">1</span>], [x, y+<span class="number">1</span>]]:</span><br><span class="line"> <span class="keyword">if</span> <span class="number">0</span><=x_<rows <span class="keyword">and</span> <span class="number">0</span><=y_<cols <span class="keyword">and</span> grid[x_][y_] == <span class="string">'1'</span>:</span><br><span class="line"> neighbors.append([x_, y_])</span><br><span class="line"> grid[x_][y_] = <span class="string">'0'</span></span><br><span class="line"> <span class="keyword">return</span> islands</span><br></pre></td></tr></table></figure>
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