Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.


题解:开始想到的方法比较偷懒,直接遍历一遍数组,把每个ListNode对应的值放到数组里面,然后把数组转换成BST,想来这个题的本意肯定不是这样。

自己也想到了bottom-up的方法,但是没想明白怎么个bottom-up法,真的是昨天做梦都在想=。=

今天早上终于弄懂了,用递归,不过这个递归比较难理解。

递归函数的定义是这样的 public TreeNode sortLisTreeNodeRecur(int size) ,参数size的意义可以理解为要建立的树的节点个数。用一个current变量作为linked list的游标。递归函数的实现如下:

 public TreeNode sortLisTreeNodeRecur(int size){
if(size <= 0)
return null; TreeNode left = sortLisTreeNodeRecur(size/2);
TreeNode root = new TreeNode(current.val);
current = current.next;
TreeNode right = sortLisTreeNodeRecur(size - size/2 - 1); root.left = left;
root.right = right; return root;
}

可以看到,它先递归调用自己建立整个左子树,在这个过程中,current作为全局私有变量,在左子树建立完成以后,就自动移动到根节点对应的ListNode处了,所以建立完左子树后建立根节点,后移current,然后递归的建立整个右子树。

以Linked List = 1->2->3->4->5来画图说明:

代码如下:

 /**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; next = null; }
* }
*/
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
private ListNode current;
public int getLength(ListNode head){
int answer = 0;
while(head != null){
answer++;
head = head.next;
} return answer;
}
public TreeNode sortLisTreeNodeRecur(int size){
if(size <= 0)
return null; TreeNode left = sortLisTreeNodeRecur(size/2);
TreeNode root = new TreeNode(current.val);
current = current.next;
TreeNode right = sortLisTreeNodeRecur(size - size/2 - 1); root.left = left;
root.right = right; return root;
}
public TreeNode sortedListToBST(ListNode head) {
current = head;
int size = getLength(head);
return sortLisTreeNodeRecur(size);
}
}

【leetcode刷题笔记】Convert Sorted List to Binary Search Tree的更多相关文章

  1. LeetCode(109) Convert Sorted List to Binary Search Tree

    题目 Given a singly linked list where elements are sorted in ascending order, convert it to a height b ...

  2. [LeetCode&Python] Problem 108. Convert Sorted Array to Binary Search Tree

    Given an array where elements are sorted in ascending order, convert it to a height balanced BST. Fo ...

  3. LeetCode(108) Convert Sorted Array to Binary Search Tree

    题目 Given an array where elements are sorted in ascending order, convert it to a height balanced BST. ...

  4. 【LeetCode】109. Convert Sorted List to Binary Search Tree 解题报告(Python)

    [LeetCode]109. Convert Sorted List to Binary Search Tree 解题报告(Python) 标签(空格分隔): LeetCode 作者: 负雪明烛 id ...

  5. Leetcode: Convert sorted list to binary search tree (No. 109)

    Sept. 22, 2015 学一道算法题, 经常回顾一下. 第二次重温, 决定增加一些图片, 帮助自己记忆. 在网上找他人的资料, 不如自己动手. 把从底向上树的算法搞通俗一些. 先做一个例子: 9 ...

  6. LeetCode:Convert Sorted Array to Binary Search Tree,Convert Sorted List to Binary Search Tree

    LeetCode:Convert Sorted Array to Binary Search Tree Given an array where elements are sorted in asce ...

  7. 【一天一道LeetCode】#109. Convert Sorted List to Binary Search Tree

    一天一道LeetCode 本系列文章已全部上传至我的github,地址:ZeeCoder's Github 欢迎大家关注我的新浪微博,我的新浪微博 欢迎转载,转载请注明出处 (一)题目 Given a ...

  8. [LeetCode] Convert Sorted List to Binary Search Tree 将有序链表转为二叉搜索树

    Given a singly linked list where elements are sorted in ascending order, convert it to a height bala ...

  9. [LeetCode] Convert Sorted Array to Binary Search Tree 将有序数组转为二叉搜索树

    Given an array where elements are sorted in ascending order, convert it to a height balanced BST. 这道 ...

  10. leetcode -- Convert Sorted List to Binary Search Tree

    Given a singly linked list where elements are sorted in ascending order, convert it to a height bala ...

随机推荐

  1. ubuntu下Tomcat绑定80端口

    转载自:https://www.2cto.com/os/201102/84081.html   工作环境迁移到了Ubuntu,很多东西发生了变化,比如原先配置tomcat端口.只需要配置server. ...

  2. ios 抓包工具 ios青花瓷charles

    iOS_青花瓷Charles抓包,ios青花瓷charles 使用青花瓷Charles抓取手机端的网络请求: 第一步,下载安装并打开Charles 第二步,去掉菜单[Proxy]以下的[Mac OSX ...

  3. lua table库

      整理自:http://www.cnblogs.com/whiteyun/archive/2009/08/10/1543139.html 1.table.concat(table, sep,  st ...

  4. MIC中函数和变量的声明

    c++/c使用 __declspec(target(mic))函数或变量声明 或 __attribute__((target(mic)))函数或变量声明 举例如下: __attribute__((ta ...

  5. web开发之html5---html5 动画特效舞动的雨伞

    http://www.cnblogs.com/stoneniqiu/p/4199294.html

  6. 小技巧:怎样以另外的Windows用户执行SSMS

    可能会碰到这种问题.你须要在一台机器上面使用不同的Windows账户连接到SQL Server做測试.默认情况下,你须要用不同的Windows账户登录然后測试. 实际上不须要每一个windows登陆. ...

  7. ztreeSearch

    $.fn.extend({ ztreeSearch : function(options) { // var _self=$(this); var defaults = { id : '', sear ...

  8. 安装Hadoop 1.1.2 (三 安装配置Hadoop)

    1 tar -zxvf hadoop-1.1.2.tar.gz 2 在hadoop/conf目录 (1) 编辑 hadoop-env.sh export JAVA_HOME=/usr/java/jdk ...

  9. tomcat下发布项目,遇到的问题总结

    以前一直是在eclipse下启动tomcat,然后访问web项目.今天脑门一热,就想用tomcat的bin目录下的startup.bat来启动tomcat,虽然tomcat的启动很顺利,但是访问网页的 ...

  10. SQL SERVER 查看表是否存在

    查看表是否存在 if exists(select 1 from sysobjects where id = OBJECT_ID('数据库名称.dbo.表明称')) drop table 为字段添加注释 ...