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RSS订阅原创 O(1) 时间复杂度的抽奖算法 - The Alias Method
使用 Vose‘s Alias Method，我们可以实现初始化为 O(n) 的算法，采样 O(1) 时间复杂度，空间负责度 O(n)。如果抽奖的奖品不考虑库存，那么可以抽奖算法就是 O(1) 事件复杂度。每次考虑库存，抽奖物品的种类变动，直接动态生成即可。
2023-04-14 01:41:07
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原创 [读书笔记] 重构 - 改善既有代码的设计第二版
refactoring-cheat-sheet《重构 改善既有代码的设计第二版》中文版注意：《重构》书籍中的代码示范，有些展示的不合理，没有与文字解释同步好第 1 章 重构，第一个示例将业务流转逻辑与计算逻辑拆分，简单点说，流转逻辑中使用的计算参数使用计算函数进行拆分出来，消除局部变量。在重构和添加新特性之间寻找平衡。重复的代码片段需要进行提取，抽象成公共的函数，便于维护。代码复审有助于在开发团队中传播知识，也有助于让较有经验的开发者把知识传递给比较欠缺经验的人，并帮助更多人理解大型软件系.
2021-12-02 18:15:36
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原创 几种对象模型的说明（PO、DTO、VO、BO、DO）
po - persistant object - 持久对象，与实体表一一对应dto - data transfer object - 数据传输对象，其中的数据用于前端展示，可以被vo进行业务转述vo - value object - 值对象，可以根据展示需求对dto中的字段进行删减和业务解释bo - business object - 业务对象，po的组合，可以包含业务的辅助计算数据，dto一般是bo中的一部分do - data object
2021-09-24 11:15:33
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原创 go 语言中关于数组值传递的一些疑惑
数组的值传递在 go 语言中数组是一个值类型（value type）所有的值类型变量在赋值和作为参数传递时都将产生一次复制动作。如果将数组作为函数的参数类型，则在函数调用时该参数将发生数据复制。因此，在函数体中无法修改传入的数组的内容，因为函数内操作的只是所传入数组的一个副本func main(){ array := []int{1, 2, 3, 4, 5, 6, 7, 8, 9} fmt.Println("in function main, array values: ", array)
2021-08-10 11:47:22
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原创 [算法题：如何让随机点亮的循环排列的100盏灯全部点亮]
本题来源于一算法同学的面试题第一想到使用数组，因为存在循环排列，觉得构造循环链表更不错，写完感觉可能还是使用数组简洁些/** * 算法题：一个圆环上有100个灯泡，灯泡有打开和关闭两种状态，灯泡的状态随机， * 按一个灯泡的开关，相邻的两个灯泡的状态也发生一次变化。 * 比如暗-亮-暗，按中间灯泡，变化为亮-暗-亮。问设计一道算法，使得所有灯泡最后都亮。 */struct Node { int state; Node* next = nullptr; Node() {}
2021-06-21 19:57:33
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原创 使用 postman 进行测试时，出现没有权限进行访问，需要配置 cookie
step1：点击红框中的 Cookiesstep2：将主域名填写好（比如 https://www.baidu.com），然后点击 Add 按钮step3：点击按钮 Add Cookie，我这边需要去预发（线上）环境拿到 token （token 的形式是：token=xxx;）后复制进去替换第一个框中的内容，然后点击第 2 个框 Save 即可。...
2021-05-18 17:36:27
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原创 修改数据库表中字段的时间值
1、修改为特定的时间update tableName set create_time = '2021-05-01 14:00:00' where id = 1;2、修改为15天前的时间update tableNameset create_time = create_time - interval 15 daywhere id = 1;
2021-05-13 14:56:20
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原创 C++ 中的 istringstream 流使用
#include <iostream>#include <sstream>using namespace std;int main(int argc, const char * argv[]) { string expression = "2-1-1"; int num = 0; char op = ' '; istringstream is(expression + '+'); while(is >> num &&a
2021-05-11 20:17:06
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原创 Mysql 将日期和时间拼接起来传入表中 timestamp 类型的字段
- 只会保留 datefield，不管 timefield 是什么，最后数据库中 timefield 都为 00:00:00concat(datefield,' ',timefield) as date- 保留日期和时间concat(datefield,' ',timefield) as date/datetime- 2021-01-01 00:00:00cast(concat('2021-01-01', ' ', '20', ':00:00') as date)- 2021-01-01
2021-05-07 17:01:05
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原创 使用python发送复杂邮件
使用python发送邮件# !/usr/bin/python# -*- coding: UTF-8 -*-# 遇到没有执行权限，使用 chmod a+x SendEmail.py import smtplibfrom email.mime.text import MIMETextfrom email.mime.multipart import MIMEMultipartfrom email.utils import formataddrfrom email.mime.image impor
2021-03-04 19:23:26
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原创 [Mac] 为mac自带的QuickTime Player播放器设置快进快退
【step1】点击启动台 -> 点击自动操作【step2】点击快速操作【step3】更改如下输入框内容【step 4】新建快进的AppleScript【step 5】1-复制如下代码片段，2-点小锤子编译on run {input, parameters} set step to 5 tell application "QuickTime Player" if front document exists th...
2020-11-22 23:32:07
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原创 图文详解KMP算法（C++，Java实现）
KMP整体算法图解：buildMatch算法图解：match[?]：match[match[j-1]]//O(n+m)#include<bits/stdc++.h>using namespace std;//针对pattern字符串建立match数组，match[j]记录从0-j位置能最最大匹配元素的位置ivoid buildMatch(strin...
2020-11-15 16:46:10
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原创 Android Studio未识别Java文件（出现红J）
随便网上找了一张图片，但问题是一样的，因为Sync完之后，无法截图了！Sync一下Sync完成后全部正常！
2020-11-06 16:05:06
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原创 在Mac上配置Android studio的adb
问题：Mac上安装完Android Studio之后，打开终端输入adb，显示没有adb: command not found方法：如下所示// 进入当前用户目录echo $HOME// 创建一个.bash_profile文件（若已经存在此文件，什么都不做）touch .bash_profile// 打开.bash_profile文件open -e .bash_profile/***打开的.bash_profile文件***/···// 文件尾部追加以下环境变量exp
2020-11-03 15:33:42
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原创 Using different JDK locations on different processes might cause Gradle to spawn multiple daemon
错误描述Android Studio is using the following JDK location when running Gradle: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home Using different JDK locations on different processes might cause Gradle to spawn multiple daemons, ..
2020-10-27 14:29:29
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原创 1319. Number of Operations to Make Network Connected
https://leetcode.com/problems/number-of-operations-to-make-network-connected/There arencomputers numbered from0ton-1connected byethernet cablesconnectionsforming a network whereconnections[i] = [a, b]represents a connection between computersa...
2020-10-22 20:21:58
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原创 1584. Min Cost to Connect All Points [Medium]
https://leetcode.com/problems/min-cost-to-connect-all-points/You are given an arraypointsrepresenting integer coordinates of some points on a 2D-plane, wherepoints[i] = [xi, yi].The cost of connecting two points[xi, yi]and[xj, yj]is themanhatta...
2020-10-22 00:40:41
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原创 不使用额外空间的情况下实现两数交换
基本原理：数字a与数字a异或结果为0。基于此，首先让 a= a ^ b，然后 b= a ^ b= (a ^ b) ^ b = a，最后，a = a ^ b = (a ^ b) ^ a = b（注意原来的b对应现在的a了）。package com.ly.test;public class MyTest { public static void main(String[] args) { int a = -2020; int b = 2020; ...
2020-10-19 15:57:48
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原创 Java InputStream.read()读取数据流字节，存储到缓冲区数组
定义public abstract int read()public int read(byte[] b)public int read(byte[] b,int off,int len)参数：b：存储读入数据的缓冲区;off:数组 b 中将写入数据的初始偏移量；len：要读取的最大字节数返回：读入缓冲区的总字节数；如果因为已经到达流末尾而不再有数据可用，则返回 -1。异常抛出：IOException: 如果不是因为流位于文件末尾而无法读取第一个字节；如果输入..
2020-10-08 17:50:07
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原创 2020-10-08
能出现问题说明：Maven静态资源过滤问题<resources> <resource> <directory>src/main/java</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include>
2020-10-08 05:45:06
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原创 2020-10-08
能出现问题说明：Maven静态资源过滤问题 src/main/java /*.properties /.xml false src/main/resources **/.properties **/*.xml false
2020-10-08 05:43:19
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原创 [Mac] MySQL Community Server 8.0.21 安装
官方下载地址步骤1：下载步骤2：安装下载下来之后直接双击安装可能会出现【无法打开“mysql-8.0.21-macos10.15-x86_64.pkg”，因为Apple无法检查其是否包含恶意软件。】解决方法：设置 - 安全性与隐私接下来一直下一步【注意中间弹出输入密码操作，设置好密码，请记住，后面登陆需要】安装完成后，设置的系统偏好界面下放有个MySQL标志。【启动】点击这标记，勾选Start MySQL when your computer st..
2020-10-07 20:00:20
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原创 665. Non-decreasing Array [Easy]
https://leetcode.com/problems/non-decreasing-array/Given an arraynumswithnintegers, your task is to check if it could become non-decreasing by modifyingat most1element.We define an array is non-decreasing ifnums[i] <= nums[i + 1]holds for e...
2020-10-04 17:22:41
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原创 1367. Linked List in Binary Tree [Medium]
https://leetcode.com/problems/linked-list-in-binary-tree/Given a binary treerootand alinked list withheadas the first node.Return True if all the elements in the linked list starting from theheadcorrespond to somedownward pathconnected in the...
2020-10-04 16:38:35
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原创 380. Insert Delete GetRandom O(1) [Medium]
https://leetcode.com/problems/insert-delete-getrandom-o1/Implement theRandomizedSetclass:bool insert(int val)Inserts an itemvalinto the set if not present. Returnstrueif the item was not present,falseotherwise. bool remove(int val)Removes an...
2020-10-04 04:49:52
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原创 560. Subarray Sum Equals K [Medium]
https://leetcode.com/problems/subarray-sum-equals-k/Given an array of integers and an integerk, you need to find the total number of continuous subarrays whose sum equals tok.Example 1:Input:nums = [1,1,1], k = 2Output: 2Constraints:The leng..
2020-10-03 23:38:48
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原创 830. Positions of Large Groups [Easy]
https://leetcode.com/problems/positions-of-large-groups/In a stringsof lowercase letters, these letters form consecutive groups of the same character.For example, a string likes = "abbxxxxzyy"has the groups"a","bb","xxxx","z", and"yy".A gro...
2020-10-03 22:24:12
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原创 229. Majority Element II [Medium]
https://leetcode.com/problems/majority-element-ii/Given an integer array of sizen, find all elements that appear more than⌊ n/3 ⌋times.Follow-up:Could you solve the problemin linear time and in O(1) space ?Example 1:Input: nums = [3,2,3]Outp...
2020-10-03 01:38:26
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原创 1379. Find a Corresponding Node of a Binary Tree in a Clone of That Tree [Medium]
https://leetcode.com/problems/find-a-corresponding-node-of-a-binary-tree-in-a-clone-of-that-tree/Given two binary treesoriginalandclonedand given a reference to a nodetargetin the original tree.Theclonedtree is acopy oftheoriginaltree.Ret...
2020-10-03 00:19:42
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原创 1110. Delete Nodes And Return Forest [Medium]
https://leetcode.com/problems/delete-nodes-and-return-forest/submissions/Given therootof a binary tree, each node in the tree has a distinct value.After deletingall nodes with a value into_delete, we are left with a forest (adisjoint union of tree...
2020-10-02 18:50:39
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原创 998. Maximum Binary Tree II [Medium]
https://leetcode.com/problems/maximum-binary-tree-ii/We are given therootnode of amaximum tree:a tree where every node has a value greater than any other value in its subtree.Just as in theprevious problem, the given treewas constructed from an l...
2020-10-01 23:23:37
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原创 1145. Binary Tree Coloring Game [Medium]
https://leetcode.com/problems/binary-tree-coloring-game/Two players play a turn based game on a binary tree. We are giventherootof this binary tree, and the number of nodesnin the tree.nis odd, andeach node has a distinct value from1ton.In...
2020-10-01 22:06:02
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原创 695. Max Area of Island [Medium]
https://leetcode.com/problems/max-area-of-island/Given a non-empty 2D arraygridof 0's and 1's, anislandis a group of1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded ...
2020-10-01 17:51:31
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原创 971. Flip Binary Tree To Match Preorder Traversal [Medium]
https://leetcode.com/problems/flip-binary-tree-to-match-preorder-traversal/Given a binary tree withNnodes, each node has a different value from{1, ..., N}.A node in this binary tree can beflippedby swapping the left child and the right child of th...
2020-10-01 17:22:21
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原创 1123. Lowest Common Ancestor of Deepest Leaves [Medium]
https://leetcode.com/problems/lowest-common-ancestor-of-deepest-leaves/Given a rooted binary tree, return the lowest common ancestor of its deepest leaves.Recall that:The node of a binary tree is aleafif and only if it has no children Thedepthof...
2020-10-01 14:34:30
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原创 1325. Delete Leaves With a Given Value [Medium]
https://leetcode.com/problems/delete-leaves-with-a-given-value/Given a binary treerootand an integertarget, delete all theleaf nodeswith valuetarget.Notethat once you delete a leaf node with valuetarget,if it's parent node becomes a leaf node ...
2020-10-01 03:56:24
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原创 979. Distribute Coins in Binary Tree [Medium]
979. Distribute Coins in Binary Tree [Medium]Given the root of a binary tree with N nodes, each node in the tree has node.val coins, and there are N coins total.In one move, we may choose two adjacent nodes and move one coin from one node to another. (T
2020-10-01 01:04:09
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