leeteCode刷题技巧

亦凉 2023-10-11 17:01 7阅读 0赞

#### 文章目录 ####

*  常用知识点
 *  1.二分查找
 *  2.排序问题
 *   *  2.1 双指针法
 *  3.数组
 *  4.动态规划
 *  5.滑动窗口
 *  6.广度优先搜索 / 深度优先搜索
 *   *  广度优先搜索（BFS）
     *  深度优先搜索（DFS）
 *  7.递归/回溯
 *  7.位运算

本文持续更新，希望和大家共同进步，欢迎探讨   
我们在进leeteCode进行刷题时不要盲目的去刷，而是有技巧有意识的去判断自己所做的题目属于哪一种类别，同时牢记不同类别的出题方式

> 如：题目的前提是数组为有序数组，同时题目还强调数组中无重复元素，因为一旦有重复元素，使用二分查找法返回的元素下标可能不是唯一的，这些都是使用二分法的前提条件，当大家看到题目描述满足如上条件的时候，可要想一想是不是可以用二分法了。

诸如此类的操做，接下来我开始带着大家进入算法的乐园  
首先看看我们的题目大概分为哪几类  
![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAWk5pbmVTdW4_size_20_color_FFFFFF_t_70_g_se_x_16_pic_center][]  
注意：本文的通用类，如ListNode的定义均在common包中  
[点击此处查找][Link 1]

## 常用知识点 ##

int []nums={
        2,1,5,3,7,9,0}
    int max=Arrays.stream(nums).max().getAsInt();//数组获取最大值
    List<Integer> list=//数组转list

## 1.二分查找 ##

做题思路：

> 利用逼近的方法逐渐靠近我们需要的结果，首先设置高低位，通过与mid即中间值的对比来进行相应的操作

题目类型：

> 一般对有序的数组进行操作时可以先考虑使用二分查找法

题目实例：

第一阶段

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>704</td> 
   <td>二分查找</td> 
   <td>https://leetcode-cn.com/problems/binary-search/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BA%8C%E5%88%86%E6%9F%A5%E6%89%BE/%E4%BA%8C%E5%88%86%E6%9F%A5%E6%89%BE_704.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>278</td> 
   <td>第一个错误版本</td> 
   <td>https://leetcode-cn.com/problems/first-bad-version/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BA%8C%E5%88%86%E6%9F%A5%E6%89%BE/%E7%AC%AC%E4%B8%80%E4%B8%AA%E9%94%99%E8%AF%AF%E7%89%88%E6%9C%AC_278.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>35</td> 
   <td>搜索插入位置</td> 
   <td>https://leetcode-cn.com/problems/search-insert-position/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BA%8C%E5%88%86%E6%9F%A5%E6%89%BE/%E6%90%9C%E7%B4%A2%E6%8F%92%E5%85%A5%E4%BD%8D%E7%BD%AE_35.java" rel="nofollow">点击查看</a></td> 
  </tr> 
 </tbody> 
</table>

--------------------

第二阶段

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
   <th>题目详解</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>34</td> 
   <td>在排序数组中查找元素的第一个和最后一个位置</td> 
   <td>https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BA%8C%E5%88%86%E6%9F%A5%E6%89%BE/%E5%9C%A8%E6%8E%92%E5%BA%8F%E6%95%B0%E7%BB%84%E4%B8%AD%E6%9F%A5%E6%89%BE%E5%85%83%E7%B4%A0%E7%9A%84%E7%AC%AC%E4%B8%80%E4%B8%AA%E5%92%8C%E6%9C%80%E5%90%8E%E4%B8%80%E4%B8%AA%E4%BD%8D%E7%BD%AE_34.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>33</td> 
   <td>搜索旋转排序数组</td> 
   <td>https://leetcode-cn.com/problems/search-in-rotated-sorted-array/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BA%8C%E5%88%86%E6%9F%A5%E6%89%BE/%E6%90%9C%E7%B4%A2%E6%97%8B%E8%BD%AC%E6%8E%92%E5%BA%8F%E6%95%B0%E7%BB%84_33.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>74</td> 
   <td>搜索二维矩阵</td> 
   <td>https://leetcode-cn.com/problems/search-a-2d-matrix/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BA%8C%E5%88%86%E6%9F%A5%E6%89%BE/%E6%90%9C%E7%B4%A2%E4%BA%8C%E7%BB%B4%E7%9F%A9%E9%98%B5_74.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>153</td> 
   <td>寻找旋转排序数组中的最小值</td> 
   <td>https://leetcode-cn.com/problems/find-minimum-in-rotated-sorted-array/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BA%8C%E5%88%86%E6%9F%A5%E6%89%BE/%E5%AF%BB%E6%89%BE%E6%97%8B%E8%BD%AC%E6%8E%92%E5%BA%8F%E6%95%B0%E7%BB%84%E4%B8%AD%E7%9A%84%E6%9C%80%E5%B0%8F%E5%80%BC_153.java" rel="nofollow">点击查看</a></td> 
   <td><a href="https://blog.csdn.net/zhiyikeji/article/details/123613185" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>162</td> 
   <td>寻找峰值</td> 
   <td>https://leetcode-cn.com/problems/find-peak-element/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BA%8C%E5%88%86%E6%9F%A5%E6%89%BE/%E5%AF%BB%E6%89%BE%E5%B3%B0%E5%80%BC_162.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
 </tbody> 
</table>

## 2.排序问题 ##

### 2.1 双指针法 ###

做题思路：

> i指向起始位置，j指向终止位置。  
> 定义一个新数组result，和A数组一样的大小，让k指向result数组终止位置。  
> 如果A\[i\]\*A\[i\]<A\[j\]\*A\[j\]那么result\[k–\] = A\[j\] \* A\[j\];  
> 如果A\[i\] \* A\[i\] >= A\[j\] \* A\[j\] 那么result\[k–\] = A\[i\] \* A\[i\];  
> 总而言之一句话：务必保证K指向的位置存的都是较大的一个数  
> 如图所示：  
> ![cf9355e2ccba64445b8559afa91eef79.gif][]

题目类型：

> 数组有序的，而且最大或最小值在数组两端。

题目实例：

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>189</td> 
   <td>轮转数组</td> 
   <td>https://leetcode-cn.com/problems/rotate-array/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E6%9C%89%E5%BA%8F%E6%95%B0%E7%BB%84%E7%9A%84%E5%B9%B3%E6%96%B9_977.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>977</td> 
   <td>有序数组的平方</td> 
   <td>https://leetcode-cn.com/problems/squares-of-a-sorted-array/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E8%BD%AE%E8%BD%AC%E6%95%B0%E7%BB%84_189.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>283</td> 
   <td>移动0</td> 
   <td>https://leetcode-cn.com/problems/move-zeroes/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E8%BD%AE%E8%BD%AC%E6%95%B0%E7%BB%84_189.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>167</td> 
   <td>两数之和 II - 输入有序数组</td> 
   <td>https://leetcode-cn.com/problems/two-sum-ii-input-array-is-sorted/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E4%B8%A4%E6%95%B0%E4%B9%8B%E5%92%8C_%E8%BE%93%E5%85%A5%E6%9C%89%E5%BA%8F%E6%95%B0%E7%BB%84_167.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>344</td> 
   <td>反转字符串</td> 
   <td>https://leetcode-cn.com/problems/reverse-string/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E5%8F%8D%E8%BD%AC%E5%AD%97%E7%AC%A6%E4%B8%B2_344.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>557</td> 
   <td>反转字符串中的单词 III</td> 
   <td>https://leetcode-cn.com/problems/reverse-words-in-a-string-iii/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E5%8F%8D%E8%BD%AC%E5%AD%97%E7%AC%A6%E4%B8%B2%E4%B8%AD%E7%9A%84%E5%8D%95%E8%AF%8D_557.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>876</td> 
   <td>链表的中间结点</td> 
   <td>https://leetcode-cn.com/problems/middle-of-the-linked-list/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E9%93%BE%E8%A1%A8%E7%9A%84%E4%B8%AD%E9%97%B4%E7%BB%93%E7%82%B9_876.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>19</td> 
   <td>删除链表第N个结点</td> 
   <td>https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E5%8C%BA%E9%97%B4%E5%88%97%E8%A1%A8%E7%9A%84%E4%BA%A4%E9%9B%86_986.java" rel="nofollow">点击查看</a></td> 
  </tr> 
 </tbody> 
</table>

--------------------

第二阶段

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
   <th>题目详解</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>82</td> 
   <td>删除排序链表中的重复元素2</td> 
   <td>https://leetcode-cn.com/problems/remove-duplicates-from-sorted-list-ii/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E5%88%A0%E9%99%A4%E6%8E%92%E5%BA%8F%E9%93%BE%E8%A1%A8%E4%B8%AD%E7%9A%84%E9%87%8D%E5%A4%8D%E5%85%83%E7%B4%A02_82.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>15</td> 
   <td>三数之和</td> 
   <td>https://leetcode-cn.com/problems/3sum/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E4%B8%89%E6%95%B0%E4%B9%8B%E5%92%8C_15.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>844</td> 
   <td>比较含退格的字符串</td> 
   <td>https://leetcode-cn.com/problems/backspace-string-compare/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E6%AF%94%E8%BE%83%E5%90%AB%E9%80%80%E6%A0%BC%E7%9A%84%E5%AD%97%E7%AC%A6%E4%B8%B2_844.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>11</td> 
   <td>盛最多水的容器</td> 
   <td>https://leetcode-cn.com/problems/container-with-most-water/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E7%9B%9B%E6%9C%80%E5%A4%9A%E6%B0%B4%E7%9A%84%E5%AE%B9%E5%99%A8_11.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>986</td> 
   <td>区间列表的交集</td> 
   <td>https://leetcode-cn.com/problems/interval-list-intersections/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%8E%92%E5%BA%8F/%E5%8F%8C%E6%8C%87%E9%92%88%E6%B3%95/%E5%8C%BA%E9%97%B4%E5%88%97%E8%A1%A8%E7%9A%84%E4%BA%A4%E9%9B%86_986.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
 </tbody> 
</table>

## 3.数组 ##

做题思路：

> 此类题目我们一般采用哈希表或相邻元素比较等方式来实现

题目实例：

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>217</td> 
   <td>存在重复元素</td> 
   <td>https://leetcode-cn.com/problems/contains-duplicate/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%95%B0%E7%BB%84/%E5%AD%98%E5%9C%A8%E9%87%8D%E5%A4%8D%E5%85%83%E7%B4%A0_217.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>1</td> 
   <td>两数之和</td> 
   <td>https://leetcode-cn.com/problems/two-sum/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%95%B0%E7%BB%84/%E4%B8%A4%E6%95%B0%E4%B9%8B%E5%92%8C_1.java" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>88</td> 
   <td>合并两个有序数组</td> 
   <td>https://leetcode-cn.com/problems/merge-sorted-array/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%95%B0%E7%BB%84/%E5%90%88%E5%B9%B6%E6%9C%89%E5%BA%8F%E6%95%B0%E7%BB%84_88.java" rel="nofollow">点击查看</a></td> 
  </tr> 
 </tbody> 
</table>

## 4.动态规划 ##

做题思路：

> 动态规划的思想通过解决了一个一个简单的问题，进而把简单的问题的解组成了复杂的问题的解

题目实例：

第一阶段

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
   <th>题目详解</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>53</td> 
   <td>最大子数组和</td> 
   <td>https://leetcode-cn.com/problems/maximum-subarray/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E5%8A%A8%E6%80%81%E8%A7%84%E5%88%92/%E6%9C%80%E5%A4%A7%E5%AD%90%E6%95%B0%E7%BB%84%E5%92%8C_53.java" rel="nofollow">点击查看</a></td> 
   <td><a href="https://blog.csdn.net/zhiyikeji/article/details/123055967" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>77</td> 
   <td>爬楼梯</td> 
   <td>https://leetcode-cn.com/problems/climbing-stairs/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E5%8A%A8%E6%80%81%E8%A7%84%E5%88%92/%E7%88%AC%E6%A5%BC%E6%A2%AF_77.java" rel="nofollow">点击查看</a></td> 
   <td><a href="https://blog.csdn.net/zhiyikeji/article/details/123498027" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>198</td> 
   <td>打家劫舍</td> 
   <td>https://leetcode-cn.com/problems/house-robber/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E5%8A%A8%E6%80%81%E8%A7%84%E5%88%92/%E6%89%93%E5%AE%B6%E5%8A%AB%E8%88%8D_198.java" rel="nofollow">点击查看</a></td> 
   <td><a href="https://blog.csdn.net/zhiyikeji/article/details/123503567" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>120</td> 
   <td>三角形最小路径和</td> 
   <td>https://leetcode-cn.com/problems/triangle/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E5%8A%A8%E6%80%81%E8%A7%84%E5%88%92/%E4%B8%89%E8%A7%92%E5%BD%A2%E6%9C%80%E5%B0%8F%E8%B7%AF%E5%BE%84%E5%92%8C_120.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
 </tbody> 
</table>

## 5.滑动窗口 ##

做题思路：

> 什么是滑动窗口？  
> 就是将元素一个又一个的放入队列中，其中队列就是我们所说的窗口，如**无重复字符的最长子串**中abcabcbb的最长子串:
> 
>  *  当abc依次进入队列之后，此时的最大值max=3
>  *  a又进入了一次，此时我们就会向后滑动一格，即从b最为起始点计算最长无重复的子串，即bca，max=3
>  *  当b进入之后继续向后滑动一格变为cab，计算无重复子序列值为3（即max=3）
>  *  c进入之后，同理，继续向后滑动一格，变为abc，计算无重复子序列值为3（即max=3）
>  *  b再次进入之后，队列继续向后滑动两格变为cb，注意此处滑动了两格，原因就是需要将已经出现的元素滑动出去，原本队列里是abc，此时只有连续滑动两个才能将b滑动出队列，此时的最大子序列长度变为2，max继续保留原有的最大值3,（注意：只有遇到更大的值才需要更换max的值，因为我们求得就是最长无重复子序列）
>  *  b在次进入，我们同样需要滑动两格将b滑动出去，此时队列变为b，这种情况下的最长序列变为1，max仍保留原值3  
>     至此滑动窗口的全部过程就结束了

题目实例：

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
   <th>题目详解</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>3</td> 
   <td>无重复字符的最长子串</td> 
   <td>https://leetcode-cn.com/problems/longest-substring-without-repeating-characters/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%BB%91%E5%8A%A8%E7%AA%97%E5%8F%A3/%E6%97%A0%E9%87%8D%E5%A4%8D%E5%AD%97%E7%AC%A6%E7%9A%84%E6%9C%80%E9%95%BF%E5%AD%90%E4%B8%B2_3.java" rel="nofollow">点击查看</a></td> 
   <td>解析参考解题思路的过程</td> 
  </tr> 
  <tr> 
   <td>567</td> 
   <td>字符串的排列</td> 
   <td>https://leetcode-cn.com/problems/permutation-in-string/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%BB%91%E5%8A%A8%E7%AA%97%E5%8F%A3/%E5%AD%97%E7%AC%A6%E4%B8%B2%E7%9A%84%E6%8E%92%E5%88%97_567.java" rel="nofollow">点击查看</a></td> 
   <td>在代码的注释中</td> 
  </tr> 
 </tbody> 
</table>

第二阶段

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
   <th>题目详解</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>438</td> 
   <td>找到字符串中所有字母异位词</td> 
   <td>https://leetcode-cn.com/problems/find-all-anagrams-in-a-string/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%BB%91%E5%8A%A8%E7%AA%97%E5%8F%A3/%E4%B9%98%E7%A7%AF%E5%B0%8F%E4%BA%8EK%E7%9A%84%E5%AD%90%E6%95%B0%E7%BB%84_713.java" rel="nofollow">点击查看</a></td> 
   <td>解析参考解题思路的过程</td> 
  </tr> 
  <tr> 
   <td>713</td> 
   <td>乘积小于K的子数组</td> 
   <td>https://leetcode-cn.com/problems/subarray-product-less-than-k/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%BB%91%E5%8A%A8%E7%AA%97%E5%8F%A3/%E4%B9%98%E7%A7%AF%E5%B0%8F%E4%BA%8EK%E7%9A%84%E5%AD%90%E6%95%B0%E7%BB%84_713.java" rel="nofollow">点击查看</a></td> 
   <td>在代码的注释中</td> 
  </tr> 
  <tr> 
   <td>209</td> 
   <td>长度最小的子数组</td> 
   <td>https://leetcode-cn.com/problems/minimum-size-subarray-sum/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%BB%91%E5%8A%A8%E7%AA%97%E5%8F%A3/%E9%95%BF%E5%BA%A6%E6%9C%80%E5%B0%8F%E7%9A%84%E5%AD%90%E6%95%B0%E7%BB%84_209.java" rel="nofollow">点击查看</a></td> 
   <td>在代码的注释中</td> 
  </tr> 
 </tbody> 
</table>

## 6.广度优先搜索 / 深度优先搜索 ##

做题思路：

### 广度优先搜索（BFS） ###

> 广度优先遍历的本质就是层次遍历，使用BFS可以求解非带权图的单源最短路径问题，这是由于 BFS总是按照距离由近到远来遍历图中的每一个顶点的性质决定的，下面 我们具体以一个实际的图进行操作。  
> ![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAWk5pbmVTdW4_size_10_color_FFFFFF_t_70_g_se_x_16_pic_center][]  
> 具体广度优先遍历的流程如下：
> 
>  *  a入队，a出队，此时a的后继结点bc入队：队列元素为：bc,结果：a
>  *  b出队，b的后继结点d,e入队：队列元素为：cde，结果：ab
>  *  c出队，c的后继结点f,g入队：队列元素为：defg，结果：abc
>  *  d出队，d无后继结点：队列元素为：efg，结果：abcd
>  *  e出队，e的后继结点h入队：队列元素为：fgh，结果：abcde
>  *  f出队，f无后继节点：队列元素为：gh,结果：abcdef
>  *  g出队，g无后继节点：队列元素为：h,结果：abcdefg
>  *  h出队，h无后继节点：队列元素为：空,结果：abcdefgh,由于队列为空，遍历结束

BFS 使用队列，把每个还没有搜索到的点依次放入队列，然后再弹出队列的头部元素当做当前遍历点。BFS 总共有两个模板：

*  1.如果不需要确定当前遍历到了哪一层，BFS 模板如下。

while queue 不空：
        cur = queue.pop()
        for 节点 in cur的所有相邻节点：
            if 该节点有效且未访问过：
                queue.push(该节点)

*  2.如果要确定当前遍历到了哪一层，BFS 模板如下。  
    这里增加了 level 表示当前遍历到二叉树中的哪一层了，也可以理解为在一个图中，现在已经走了多少步了。size 表示在当前遍历层有多少个元素，也就是队列中的元素数，我们把这些元素一次性遍历完，即把当前层的所有元素都向外走了一步。

level = 0
    while queue 不空：
        size = queue.size()
        while (size -->0) {
        
            cur = queue.pop()
            for 节点 in cur的所有相邻节点：
                if 该节点有效且未被访问过：
                    queue.push(该节点)
        }
        level ++;

### 深度优先搜索（DFS） ###

> 深度优先搜索类似于树的先序遍历，同样，我们具体以一个实际的图进行操作。  
> ![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAWk5pbmVTdW4_size_10_color_FFFFFF_t_70_g_se_x_16_pic_center][]  
> 具体广度优先遍历的流程如下：
> 
>  *  a出，a有后继节点b，b出，b有后继结点d，d出：abd
>  *  d无后继结点，回退到b，b有后继结点d,e但d已经访问过了，e出：abde，e有后继结点h，h出：abdeh
>  *  h无后继结点，回退e，e有后继结点h，但h已经 访问继续回退，回退到b，b的后继结点也全部被访问，继续回退，回退到a，访问后继结点c：abdehc
>  *  c有后继结点f，访问f：abdehcf
>  *  f无后继结点，回退到c，访问另一个 后继结点g：abdehcfg
>  *  结点全部访问，遍历结束

题目实例：

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
   <th>题目详解</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>733</td> 
   <td>图像渲染</td> 
   <td>https://leetcode-cn.com/problems/flood-fill/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E5%9B%BE%E5%83%8F%E6%B8%B2%E6%9F%93_733.java" rel="nofollow">点击查看</a></td> 
   <td><a href="https://blog.csdn.net/zhiyikeji/article/details/123189260" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>617</td> 
   <td>合并二叉树</td> 
   <td>https://leetcode-cn.com/problems/merge-two-binary-trees/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E5%90%88%E5%B9%B6%E4%BA%8C%E5%8F%89%E6%A0%91_617.java" rel="nofollow">点击查看</a></td> 
   <td>请参考代码注释解析</td> 
  </tr> 
  <tr> 
   <td>116</td> 
   <td>填充每个节点的下一个右侧节点指针</td> 
   <td>https://leetcode-cn.com/problems/populating-next-right-pointers-in-each-node/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E5%A1%AB%E5%85%85%E6%AF%8F%E4%B8%AA%E8%8A%82%E7%82%B9%E7%9A%84%E4%B8%8B%E4%B8%80%E4%B8%AA%E5%8F%B3%E4%BE%A7%E8%8A%82%E7%82%B9%E6%8C%87%E9%92%88_116.java" rel="nofollow">点击查看</a></td> 
   <td>请参考代码注释解析</td> 
  </tr> 
  <tr> 
   <td>733</td> 
   <td>图像渲染</td> 
   <td>https://leetcode-cn.com/problems/flood-fill/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E5%9B%BE%E5%83%8F%E6%B8%B2%E6%9F%93_733.java" rel="nofollow">点击查看</a></td> 
   <td>请参考代码注释解析</td> 
  </tr> 
  <tr> 
   <td>542</td> 
   <td>0 1矩阵</td> 
   <td>https://leetcode-cn.com/problems/01-matrix/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E7%9F%A9%E9%98%B501_542.java" rel="nofollow">点击查看</a></td> 
   <td><a href="https://blog.csdn.net/zhiyikeji/article/details/123273846" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>994</td> 
   <td>腐烂的橘子</td> 
   <td>https://leetcode-cn.com/problems/rotting-oranges/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E8%85%90%E7%83%82%E7%9A%84%E6%A9%98%E5%AD%90_994.java" rel="nofollow">点击查看</a></td> 
   <td>请参考01矩阵的解题思路</td> 
  </tr> 
 </tbody> 
</table>

第二阶段

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
   <th>题目详解</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>200</td> 
   <td>岛屿数量</td> 
   <td>https://leetcode-cn.com/problems/number-of-islands/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E5%B2%9B%E5%B1%BF%E6%95%B0%E9%87%8F_200.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>574</td> 
   <td>省份数量</td> 
   <td>https://leetcode-cn.com/problems/flood-fill/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E7%9C%81%E4%BB%BD%E6%95%B0%E9%87%8F_547.java" rel="nofollow">点击查看</a></td> 
   <td><a href="https://blog.csdn.net/zhiyikeji/article/details/123735520?spm=1001.2014.3001.5501" rel="nofollow">点击查看</a></td> 
  </tr> 
  <tr> 
   <td>1091</td> 
   <td>二进制矩阵中的最短路径</td> 
   <td>https://leetcode-cn.com/problems/shortest-path-in-binary-matrix/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E4%BA%8C%E8%BF%9B%E5%88%B6%E7%9F%A9%E9%98%B5%E4%B8%AD%E7%9A%84%E6%9C%80%E7%9F%AD%E8%B7%AF%E5%BE%84_1091.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>572</td> 
   <td>另一棵树的子树</td> 
   <td>https://leetcode-cn.com/problems/subtree-of-another-tree/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E5%8F%A6%E4%B8%80%E6%A3%B5%E6%A0%91%E7%9A%84%E5%AD%90%E6%A0%91_572.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>797</td> 
   <td>所有可能的路径</td> 
   <td>https://leetcode-cn.com/problems/all-paths-from-source-to-target/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E6%89%80%E6%9C%89%E5%8F%AF%E8%83%BD%E7%9A%84%E8%B7%AF%E5%BE%84_797.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>130</td> 
   <td>被围绕的区域</td> 
   <td>https://leetcode-cn.com/problems/surrounded-regions/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E6%B7%B1%E5%BA%A6and%E5%B9%BF%E5%BA%A6%E6%90%9C%E7%B4%A2/%E8%A2%AB%E5%9B%B4%E7%BB%95%E7%9A%84%E5%8C%BA%E5%9F%9F_130.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
 </tbody> 
</table>

## 7.递归/回溯 ##

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
   <th>题目详解</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>206</td> 
   <td>反转链表</td> 
   <td>https://leetcode-cn.com/problems/reverse-linked-list/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E9%93%BE%E8%A1%A8/%E5%8F%8D%E8%BD%AC%E9%93%BE%E8%A1%A8_206.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>21</td> 
   <td>合并两个有序链表</td> 
   <td>https://leetcode-cn.com/problems/merge-two-sorted-lists/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E9%93%BE%E8%A1%A8/%E5%90%88%E5%B9%B6%E4%B8%A4%E4%B8%AA%E6%9C%89%E5%BA%8F%E9%93%BE%E8%A1%A8_21.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>77</td> 
   <td>组合</td> 
   <td>https://leetcode-cn.com/problems/combinations/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E9%93%BE%E8%A1%A8/%E5%90%88%E5%B9%B6%E4%B8%A4%E4%B8%AA%E6%9C%89%E5%BA%8F%E9%93%BE%E8%A1%A8_21.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>46</td> 
   <td>全排列</td> 
   <td>https://leetcode-cn.com/problems/permutations/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E9%80%92%E5%BD%92And%E5%9B%9E%E6%BA%AF/%E5%85%A8%E6%8E%92%E5%88%97_46.java" rel="nofollow">点击查看</a></td> 
   <td>请务必牢记该题的解决方式，理解不了就把代码背下来，以后遇到类似的题目即可套用，同时应牢记DFS的进退栈思想</td> 
  </tr> 
  <tr> 
   <td>784</td> 
   <td>字母大小写全排列</td> 
   <td>https://leetcode-cn.com/problems/letter-case-permutation/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E9%80%92%E5%BD%92And%E5%9B%9E%E6%BA%AF/%E5%AD%97%E6%AF%8D%E5%A4%A7%E5%B0%8F%E5%86%99%E5%85%A8%E6%8E%92%E5%88%97_784.java" rel="nofollow">点击查看</a></td> 
   <td>参考代码解析</td> 
  </tr> 
 </tbody> 
</table>

## 7.位运算 ##

> 在位运算的操作者，我们需要 熟知的几个操作：
> 
>  *  1.如果(n&(n-1))==0表示n是2的幂次方
>  *  2.a<<n：表示 a左移n位，相当于  
>      a ∗ 2 n a\*2^n a∗2n
>  *  3.a>>n：表示a右移n位，相当于  
>      a ÷ 2 n a÷2^n a÷2n
>  *  4.>>= 右移赋值
>  *  5.>>>= 右移赋值，左边空出的位以0填充
>  *  6.a⊕0=a
>  *  7.a⊕a=0
>  *  8.a⊕b⊕a=b⊕a⊕a=b⊕(a⊕a)=b⊕0=b

<table> 
 <thead> 
  <tr> 
   <th>题目编号</th> 
   <th>题目名称</th> 
   <th>题目链接</th> 
   <th>代码链接</th> 
   <th>题目详解</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>231</td> 
   <td>2的幂</td> 
   <td>https://leetcode-cn.com/problems/power-of-two/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BD%8D%E8%BF%90%E7%AE%97/%E5%B9%82_2%E7%9A%84%E5%B9%82_231.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>191</td> 
   <td>位1的个数</td> 
   <td>https://leetcode-cn.com/problems/number-of-1-bits/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BD%8D%E8%BF%90%E7%AE%97/%E4%BD%8D1%E7%9A%84%E4%B8%AA%E6%95%B0_191.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>136</td> 
   <td>只出现一次的数字</td> 
   <td>https://leetcode-cn.com/problems/single-number/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BD%8D%E8%BF%90%E7%AE%97/%E5%8F%AA%E5%87%BA%E7%8E%B0%E4%B8%80%E6%AC%A1%E7%9A%84%E6%95%B0%E5%AD%97_136.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
  <tr> 
   <td>190</td> 
   <td>颠倒二进制位</td> 
   <td>https://leetcode-cn.com/problems/reverse-bits/</td> 
   <td><a href="https://gitee.com/ninesuntec/leete-code/blob/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/%E4%BD%8D%E8%BF%90%E7%AE%97/%E9%A2%A0%E5%80%92%E4%BA%8C%E8%BF%9B%E5%88%B6%E4%BD%8D_190.java" rel="nofollow">点击查看</a></td> 
   <td>暂无解析</td> 
  </tr> 
 </tbody> 
</table>

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[Link 1]: https://gitee.com/ninesuntec/leete-code/tree/master/%E4%BB%A3%E7%A0%81/src/main/java/com/exercise/leetecode/common
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