叶现一的专栏

原创 知识图谱推理思维导图

原创 Gremlin: How to connect to gremlin server console

:remote connect tinkerpop.server conf/remote.yaml:remote consolegraph = TinkerGraph.open()g = graph.traversal()g.V()# g.close()

原创 Oracle12c: How to create PDB in manually

Pre-condition: Go through my last blog.Install:Mount and open CDB sqlplus / as sysdba;startup nomount ;alter database open ;conn sys@NDLNE as sysdba ; Create PDB create pluggable database pdb1admin user pdb1_admin identified by pdb1_admin

原创 Oracle12c: How to create CDB in manually

Set ORACLE_SID, for example, NDLNE export ORACLE_SID=NDLNE Create PFILE vi /u01/app/oracle/admin/NDLNE/pfile/init.oradb_name='NDLNE'memory_target=1Gmemory_max_target=1GDB_CREATE_FILE_DEST='/u01/app/oracle/oradata'control_files='/u01/app/oracle

原创 ORA-00845: MEMORY_TARGET not supported on this system

Issue：When trying to startup Oracle Instance, you may encounter following error:ORA-00845: MEMORY_TARGET not supported on this systemRoot Cause:Your shm size is smaller than Memory_Target.Solution:Open pfile in "/u01/app/oracle/admin/<..

原创 HOWTO: install Oracle 12c Database on Centos8

Step:PrepareCentOS Linux release 8.3.2011 with 4 core, 4G RAM and 40G DIsk space at least. Download Oracle 12c fromhttps://edelivery.oracle.com/osdc/faces/SoftwareDelivery You will see several ZIP file, like following Unzip all the ZIP files to a cu..

转载 LeetCode: 974. Subarray Sums Divisible by K

MediumGiven an arrayAof integers, return the number of (contiguous, non-empty) subarrays that have a sum divisible byK.Example 1:Input: A = [4,5,0,-2,-3,1], K = 5Output: 7Explanation: There are 7 subarrays with a sum divisible by K = 5:[4, 5, ...

原创 LeetCode: 560. Subarray Sum Equals K

Given an array of integersnumsand an integerk, returnthe total number of continuous subarrays whose sum equals tok.Example 1:Input: nums = [1,1,1], k = 2Output: 2Example 2:Input: nums = [1,2,3], k = 3Output: 2Constraints:1 <= nums...

原创 LeetCode: 267. Palindrome Permutation II

MediumGiven a strings, return all the palindromic permutations (without duplicates) of it. Return an empty list if no palindromic permutation could be form.Example 1:Input: "aabb"Output: ["abba", "baab"]Example 2:Input: "abc"Output: []解法：.

原创 LeetCode：47. Permutations II

Given a collection of numbers,nums,that might contain duplicates, returnall possible unique permutationsin any order.Example 1:Input: nums = [1,1,2]Output:[[1,1,2], [1,2,1], [2,1,1]]Example 2:Input: nums = [1,2,3]Output: [[1,2,3],[1,3,2...

原创 LeetCode: 46. Permutations

MediumGiven a collection ofdistinctintegers, return all possible permutations.Example:Input: [1,2,3]Output:[ [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1]]解法：（回溯）本题要求生成全排列，那么看看我们能找到什么规律。以[1，2，3]为例，全排列是[1，2，3][1，3，2][2..

原创 LeetCode:31. Next Permutation

31.Next PermutationMediumImplementnext permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.If such an arrangement is not possible, it must rearrange it as the lowest possible order (i.e., sorted in a..

原创 性能测试结果

Dev Environmentserver.tomcat.max-threads=10server.tomcat.accept-count=100server.tomcat.min-spare-threads=10server.tomcat.max-threads=20server.tomcat.accept-count=100server.tomcat.min-spa...

原创 架构模式对比

传统垂直架构 RPC架构 SOA 微服务 架构图 优点 简单应用开发成本较小 编译测试部署发布简单 跨语言（C+...

原创 事务隔离级别

Read uncommitted Read committed Repeatable read Serializable 定义 允许一个事务可以读取另一个未提交事务的数据 一个事务只能读取另一个已提交事务的数据 ...

原创 LeetCode: 核心算法（快速选择）

场景：解决Top K问题例如：输入: [3,2,1,5,6,4] 和 k = 2输出: 5解决方法：此类问题一般都是通过一次快排或者大顶堆的方式解决，但是都有问题：快排：对全数组进行了排序，如果要寻找的是第K个大的元素，那么其实我们并不关心从小到大排序后数组的第K位之后的数字；但是快排依然对这些数字进行了排序大顶堆：虽然大顶堆的方法解决了不用考虑第K位之后的数字的问题，但是它依然需要关心第K位之前的数字，所以依然浪费了很多时间问题分析仔细想想Top K问题，其实.

原创 LeetCode: 常用API及算法

1. 小顶堆 （从小到大）Queue<Integer> heap = new PriorityQueue<>() ;2. 大顶堆 （由大到小） Queue<Integer> heap = new PriorityQueue<>((o1, o2) -> o2 - o1) ;

原创 LeetCode:215. Kth Largest Element in an Array

MediumFind thekth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.Example 1:Input: [3,2,1,5,6,4] and k = 2Output: 5Example 2:Input: [3,2,3,1,2,4,5,5,6] and k = 4.

原创 LeetCode：159. Longest Substring with At Most Two Distinct Characters

Given a string s , find the length of the longest substring t that contains at most 2 distinct characters. Example 1: Input: "eceba" Output: 3 Explanation: t is "ece" which its length is 3. Example 2: Input: "ccaabbb...

原创 Leetcode: 3. Longest Substring Without Repeating Characters

Given a strings, find the length of thelongest substringwithout repeating characters.Example 1:Input: s = "abcabcbb"Output: 3Explanation: The answer is "abc", with the length of 3.Example 2:Input: s = "bbbbb"Output: 1Explanation: The answ...

原创 Leetcode: 16. 3Sum Closest

16.3Sum ClosestMediumGiven an arraynumsofnintegers and an integertarget, find three integers innumssuch that the sum is closest totarget. Return the sum of the three integers. You may assume that each input would have exactly one solution.Ex...

原创 Leetcode: 15. 3Sum

Given an arraynumsofnintegers, are there elementsa,b,cinnumssuch thata+b+c= 0? Find all unique triplets in the array which gives the sum of zero.Notice that the solution set must not contain duplicate triplets.Example 1:Input: nums =...

原创 Leetcode: 1. Two Sum

1.Two SumEasyGiven an array of integers, returnindicesof the two numbers such that they add up to a specific target.You may assume that each input would haveexactlyone solution, and you may not use thesameelement twice.Example:Given nums ...

原创 Docker: How to config Http Proxy for accessing the Internet

Issue:When you working on docker, you may behind corporate proxy, which means that your docker container cannot access the Internet.Solution:Config Http Proxy for Docker Engine, so that all the ...

原创 Leetcode: 209. Minimum Size Subarray Sum

Given an array ofnpositive integers and a positive integers, find the minimal length of acontiguoussubarray of which the sum ≥s. If there isn't one, return 0 instead.Example:Input: s = 7, ...

原创 Leetcode: 207. Course Schedule

There are a total ofncourses you have to take, labeled from0ton-1.Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair...

原创 Leetcode:179. Largest Number

Given a list of non negative integers, arrange them such that they form the largest number.Example 1:Input: [10,2]Output: "210"Example 2:Input: [3,30,34,5,9]Output: "9534330"Note:The r...

原创 Leetcode 152:Maximum Product Subarray

Given an integer arraynums, find the contiguous subarray within an array (containing at least one number) which has the largest product.Example 1:Input: [2,3,-2,4]Output: 6Explanation:[2,3] h...

原创 Leetcode 150: Evaluate Reverse Polish Notation

Evaluate the value of an arithmetic expression inReverse Polish Notation.Valid operators are+,-,*,/. Each operand may be an integer or another expression.Note:Division between two integers ...

原创 Leetcode 148: Sort List

Sort a linked list inO(nlogn) time using constant space complexity.Example 1:Input: 4->2->1->3Output: 1->2->3->4Example 2:Input: -1->5->3->4->0Output: -1-...

原创 LeetCode 146：LRU Cache

Design and implement a data structure forLeast Recently Used (LRU) cache. It should support the following operations:getandput.get(key)- Get the value (will always be positive) of the key if th...

原创 Leetcode 143: Reorder List

143.Reorder ListGiven a singly linked listL:L0→L1→…→Ln-1→Ln,reorder it to:L0→Ln→L1→Ln-1→L2→Ln-2→…You maynotmodify the values in the list's nodes, only nodes itself may be changed.Example ...

原创 Leetcode: 139 Word Break

139.Word BreakGiven anon-emptystringsand a dictionarywordDictcontaining a list ofnon-emptywords, determine ifscan be segmented into a space-separated sequence of one or more dictionary wo...

原创 Leetcode 127: Word Ladder

127.Word LadderGiven two words (beginWordandendWord), and a dictionary's word list, find the length of shortest transformation sequence frombeginWordtoendWord, such that:Only one letter can ...

原创 Leetcode 91. Decode Ways

A message containing letters fromA-Zis being encoded to numbers using the following mapping:'A' -> 1'B' -> 2...'Z' -> 26Given anon-emptystring containing only digits, determine t...

原创 LeetCode：5. Longest Palindromic Substring

Given a strings, find the longest palindromic substring ins. You may assume that the maximum length ofsis 1000.Example 1:Input: "babad"Output: "bab"Note: "aba" is also a valid answer.Exa...

原创 LeetCode:3. Longest Substring Without Repeating Characters

3.Longest Substring Without Repeating CharactersMediumGiven a string, find the length of thelongest substringwithout repeating characters.Example 1:Input: "abcabcbb"Output: 3 Explanation...

原创 Eureka: example of creating 3 nodes Eureka Server with docker

Abstract:In this artical, it will state how to create 3 nodes Eureka Server with docker.Step1. Create Eureka ServerSource:https://github.com/yexianyi/Chukonu/tree/master/chukonu-springcloud-eur...

原创 Eureka Issue: replicas is not working

Problem:When we create 3-nods Eureka server and register them with each other, you may find the replica is not working.Reason:Each of node must have an unique"eureka.instance.hostname". Differe...

原创 Mysql Lock with different isolation level

0. PreparationCREATE TABLE `test` ( `id` int(11) DEFAULT NULL, `name` varchar(100) DEFAULT NULL, UNIQUE KEY `test_id_IDX` (`id`) USING BTREE) ENGINE=InnoDB DEFAULT CHARSET=utf8;1.Read...