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Reck Zhang

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Operating System 09 - 进程状态的切换

进程状态的切换 📷 就绪状态(ready): 等待被调度运行状态(running): 正在被调度阻塞状态(waiting): 等待资源注意只有就绪态和运行态可以相互转换, 其他都是单向转换. 就绪状态的进程通过调度算法从而获得CPU时间, 转化为运行状态. 而运行状态的进程, 在分配给他的CPU时间片用完之后就会转为就绪状态, 等待下一次调度. 阻塞状态是缺少需要的资源从而由运行状态转换而来, 但是该资源不包括CPU时间, 缺少CPU时间就会从运行状态转换为就绪态.

2021-12-23

4550

Operating System 08 - 进程与线程

block ip process 进程线程

进程控制块(Process Control Block, PCB)描述进程的基本信息和运行状态, 所谓的创建进程和撤销进程, 都是对于PCB的操作.

2021-12-23

2290

ACID 原子性(Atomicity) 事务被分割为不可分割的最小单元, 事务的所有操作要么全部提交成功, 要么全部回滚失败. 一致性(Consistency) 数据库在事务执行前后都保持一致性状态. 在一致性状态下, 所有事务对一个数据的读取结果都是相同的. 隔离性(Isolation) 一个事务所做的修改在最终提交之前, 对其他事务不可见. 持久性(Durability) 一旦事务提交, 则其所做的修改将会永远修改到数据库中. 即使系统发生崩溃, 事务执行的结果也不能丢失.

2021-12-23

1670

C++ 01 - 内存模型

内存模型堆(heap) 由new分配出来的内存块, 其释放编译器不去管, 由程序去控制, 一个new对应一个delete. 如果没有释放掉, 在程序结束时OS会自动回收. 栈(stack) 栈是那些编译器在需要时分配, 在不需要时自动清除的存储区, 存放局部变量, 函数参数. 存放的栈中的数据只在当前函数及下一层函数中有效, 一旦函数返回了, 这些数据也就自动释放. 全局/静态存储区(.bss段和.data段) 全局和静态变量被分配到同一内存中. 在C语言中, 未初始化的放在.ba

2021-12-23

3660

ACMSGURU 149 - Computer Network

input line lines network numbers

A school bought the first computer some time ago. During the recent years the school bought N-1 new computers. Each new computer was connected to one of settled earlier. Managers of school are anxious about slow functioning of the net and want to know for each computer number Si - maximum distance, for which i-th computer needs to send signal (i.e. length of cable to the most distant computer). You need to provide this information.

2021-12-18

3050

ACMSGURU 397 - Text Editor

css linux 编程算法

The simplest text editor “Open Word” allows to create and edit only one word. The editor processes keys ‘a’ – ‘z’, and also ‘L’ (to the left) and ‘R’ (to the right). After starting his work the editor immediately creates an empty word and sets its cursor to the left-most position. When one of keys ‘a’ – ‘z’ is pressed, the text editor inserts corresponding symbol just after the cursor. After that a cursor moves one position to the right in such a way that it is placed just after new symbol. When key ‘L’ or ‘R’ is pressed, the cursor moves one position to the left or to the right respectively. If the cursor can’t be moved because it is placed at the left-most or right-most position the command is ignored. Developers of “Open Word” didn’t think about the effectiveness so the editor is working slowly if a lot of keys have been pressed.

2021-12-05

5120

ACMSGURU 114 - Telecasting station

axis find input output sample

Every city in Berland is situated on Ox axis. The government of the country decided to build new telecasting station. After many experiments Berland scientists came to a conclusion that in any city citizens displeasure is equal to product of citizens amount in it by distance between city and TV-station. Find such point on Ox axis for station so that sum of displeasures of all cities is minimal.

2021-09-01

4960

LeetCode 0198 - House Robber

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have security system connected and it will automatically contact the police if two adjacent houses were broken into on the same night.

2021-08-11

2330

LeetCode 0199 - Binary Tree Right Side View

binary nodes return tree view

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

2021-08-11

2380

LeetCode 0231 - Power of Two

function integer

Given an integer, write a function to determine if it is a power of two.

2021-08-11

1330

Java 15 - 类加载过程

编程算法 ide java

确保Class文件的字节流中包含的信息符合虚拟机的要求, 并且不会危害虚拟机的安全.

2021-08-11

3480

Java 16 - 序列化与反序列化

需要进行序列化的类需要实现Serializable接口, 但是不需要实现任何方法.

2021-08-11

2550

LeetCode 0200 - Number of Islands

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

2021-08-11

3250

LeetCode 0201 - Bitwise AND of Numbers Range

numbers range return

Given a range [m, n] where 0 <= m <= n <= 2147483647, return the bitwise AND of all numbers in this range, inclusive.

2021-08-11

1950

LeetCode 0202 - Happy Number

cycle equals integer numbers process

Write an algorithm to determine if a number is “happy”.

2021-08-11

2440

LeetCode 0203 - Remove Linked List Elements

Remove all elements from a linked list of integers that have value val.

2021-08-11

2130

LeetCode 0183 - Customers Who Never Order

sql orders return table using

Suppose that a website contains two tables, the Customers table and the Orders table. Write a SQL query to find all customers who never order anything.

2021-08-11

3050

LeetCode 0184 - Department Highest Salary

sql it max table

The Employee table holds all employees. Every employee has an Id, a salary, and there is also a column for the department Id.

2021-08-11

3320

LeetCode 0185 - Department Top Three Salaries

The Employee table holds all employees. Every employee has an Id, and there is also a column for the department Id.

2021-08-11

2230

LeetCode 0187 - Repeated DNA Sequences

function series

All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: “ACGAATTCCG”. When studying DNA, it is sometimes useful to identify repeated sequences within the DNA.

2021-08-11

2920

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