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20191218——第一百题 相同的树

由 寵の児 提交于 2019-12-18 21:43:50
以后的代码要进行注释，方便理解 递归 最简单的策略是递归，首先判断p与q是不是None，然后判断它们的值是否相等，若通过以上判断，则对递归子节点做同样操作。 /** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public boolean isSameTree(TreeNode p, TreeNode q) { //如果p与q都为空，那么是相同的树 if(p ==null && q ==null){ return true; } //如果p或者q一个为空，另一个不为空，那么一定不是相同的树 if( p == null ||q==null){ return false; } //如果p与q的值不同，那么也一定不是相同的树 if(p.val != q.val){ return false; } return (isSameTree(p.right,q.right)&&isSameTree(p.left,q.left)); } } 时间复杂度是n，n是树的节点，所以每个结点都访问一次。 空间复杂度 :

Javascript nodeValue returns null

由 China☆狼群 提交于 2019-12-18 21:22:39
问题 Title should make my problem well described.Here goes my code. <div id="adiv"><text>Some text</text></div> <script type="text/javascript"> function vb(){ alert(document.getElementById("adiv").firstChild.nodeValue); //returns null } </script> <input type="button" onclick="vb();" value="get"/> wheres the problem..? 回答1: In order to get [merged] text content of an element node: function vb(){ var textnode = document.getElementById("adiv").firstChild; alert(textnode.textContent || textnode

What is the difference between a.ne(null) and a != null in Scala?

由 感情迁移 提交于 2019-12-18 18:55:58
问题 I have been always using a != null to check that a is not a null reference. But now I've met another way used: a.ne(null) what way is better and how are they different? 回答1: Like @Jack said x ne null is equal to !(x eq null) . The difference between x != null and x ne null is that != checks for value equality and ne checks for reference equality. Example: scala> case class Foo(x: Int) defined class Foo scala> Foo(2) != Foo(2) res0: Boolean = false scala> Foo(2) ne Foo(2) res1: Boolean = true

NULL和DBNull的区别分析

由 夙愿已清 提交于 2019-12-18 18:38:26
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 测试准备： 1.新建一个表 CREATE TABLE `cacb` ( `CA` varchar(255) DEFAULT NULL, `CB` varchar(255) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8; 2.新建一个控制台项目，主函数实现如下： #region Mysql DBNull测试 string con = "server=localhost;User Id=root;database=mytest;password=my88888;persist security info=True;charset=utf8;"; bool flg = null is object;//false bool fdb = DBNull.Value is object;//true string sql = "SELECT * from CACB limit 1,1;"; using (MySqlConnection mc=new MySqlConnection(con)) { mc.Open(); using (MySqlCommand com=new MySqlCommand(sql,mc)) { var result= com

Pass a NULL in a parameter to a DateTime field in a stored procedure

由 旧城冷巷雨未停 提交于 2019-12-18 15:30:55
问题 I have a stored procedure which updates a database using the parameters I supply but I'm having trouble passing a NULL to the stored procedure The field I need to make NULL is a DateTime field DB.Parameters.AddWithValue("@date", NULL) This gives me the error 'NULL' is not declared. 'Null' constant is no longer supported; use 'System.DBNull' instead So I tried DB.Parameters.AddWithValue("@date", DBNull.Value.ToString()) But this produces the value 1900-01-01 00:00:00.000 in the column as it's

Comparison operator in PySpark (not equal/ !=)

由 [亡魂溺海] 提交于 2019-12-18 15:01:13
问题 I am trying to obtain all rows in a dataframe where two flags are set to '1' and subsequently all those that where only one of two is set to '1' and the other NOT EQUAL to '1' With the following schema (three columns), df = sqlContext.createDataFrame([('a',1,'null'),('b',1,1),('c',1,'null'),('d','null',1),('e',1,1)], #,('f',1,'NaN'),('g','bla',1)], schema=('id', 'foo', 'bar') ) I obtain the following dataframe: +---+----+----+ | id| foo| bar| +---+----+----+ | a| 1|null| | b| 1| 1| | c| 1

SQL using If Not Null on a Concatenation

由 て烟熏妆下的殇ゞ 提交于 2019-12-18 14:54:35
问题 If I have the table SELECT (Firstname || '-' || Middlename || '-' || Surname) AS example_column FROM example_table This will display Firstname-Middlename-Surname e.g. John--Smith Jane-Anne-Smith The second one (Jane’s) displays correct, however since John doesn’t have a middlename, I want it to ignore the second dash. How could I put a sort of IF Middlename = NULL statement in so that it would just display John-Smith 回答1: Here would be my suggestions: PostgreSQL and other SQL databases where

How to check multiple objects for nullity?

由 别等时光非礼了梦想. 提交于 2019-12-18 13:52:58
问题 Often, I can see a code constructs like following: if(a == null || b == null || c == null){ //... } I wonder if there is any widely used library (Google, Apache, etc.) to check against nullity for multiple objects at once, e.g.: if(anyIsNull(a, b, c)){ //... } or if(allAreNulls(a, b, c)){ //... } UPDATE: I perfectly know how to write it by myself I know it can be the result of the poor program structure but it's not a case here Let's make it more challenging and replace original example with

Why is the result of adding two null strings not null? [duplicate]

由 北慕城南 提交于 2019-12-18 13:52:42
问题 This question already has answers here : Why is it Valid to Concatenate Null Strings but not to Call “null.ToString()”? (11 answers) Closed 5 years ago . I was fiddling around in C# when I came across this weird behavior in .Net programming. I have written this code: static void Main(string[] args) { string xyz = null; xyz += xyz; TestNullFunc(xyz); Console.WriteLine(xyz); Console.Read(); } static void TestNullFunc(string abc) { if (abc == null) { Console.WriteLine("meow THERE ! "); } else {

java.lang.NullPointerException: Attempt to invoke virtual method on a null object reference to select sqlite

由 淺唱寂寞╮ 提交于 2019-12-18 13:29:23
问题 I am a newbie of android world. I have a problem of the coding. It was just a tiny error buy i dont know it doesnt work even i change others method but the error still the same error. Here the error occur at logcat: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor com.example.zellon.surveyapps.DatabaseHelper.getAData()' on a null object reference I just want to select the data in the database to get an id but cant cuz of the error above. I will give a
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