ARST第三周打卡

Algorithm : 做一个 leetcode 的算法题

//二位数组查找 题目描述

//在一个二维数组中（每个一维数组的长度相同），每一行都按照从左到右递增的顺序排序，每一列都按照从上到下递增的顺序排序。

//请完成一个函数，输入这样的一个二维数组和一个整数，判断数组中是否含有该整数。

bool FindNum(int target, vector<vector<int> > vect)
{
    int iRow = vect.size();
    int iCol = vect[0].size();

    //从左上角开始遍历
    int i = 0, j = iCol - 1;
    while (i <= iRow - 1 && j >= 0) //保证数组不能越界
    {
        if (vect[i][j] > target)
        {
            j--;
        }
        else if (vect[i][j] < target)
        {
            i++;
        }
        else
        {
            return true;
        }
    }

    return false;
}

Review : 阅读并点评一篇英文技术文章

原文地址：http://download.redis.io/redis-stable/redis.conf

################################ SNAPSHOTTING ################################
#
# Save the DB on disk:
#
# save <seconds> <changes>
#
# Will save the DB if both the given number of seconds and the given
# number of write operations against the DB occurred.

根据给定的每秒多少写操作保存DB;

#
# In the example below the behaviour will be to save:
# after 900 sec (15 min) if at least 1 key changed
# after 300 sec (5 min) if at least 10 keys changed
# after 60 sec if at least 10000 keys changed
#
# Note: you can disable saving completely by commenting out all "save" lines.
#
# It is also possible to remove all the previously configured save
# points by adding a save directive with a single empty string argument
# like in the following example:
#
# save ""

save 900 1
save 300 10
save 60 10000

保存DB到磁盘：

# By default Redis will stop accepting writes if RDB snapshots are enabled
# (at least one save point) and the latest background save failed.
# This will make the user aware (in a hard way) that data is not persisting
# on disk properly, otherwise chances are that no one will notice and some
# disaster will happen.

默认情况下：如果开启了RDB快照(至少一个保存点)并且最后一个备份保存失败，那么redis将停止接受写操作；

#
# If the background saving process will start working again Redis will
# automatically allow writes again.
#
# However if you have setup your proper monitoring of the Redis server
# and persistence, you may want to disable this feature so that Redis will
# continue to work as usual even if there are problems with disk,
# permissions, and so forth.
stop-writes-on-bgsave-error yes

但是，如果你设置了对redis服务器和持久性的适当监控，你可能希望禁用这些特性以便即使存在硬盘、权限等问题，Redis也能照常工作！

# Compress string objects using LZF when dump .rdb databases?
# For default that's set to 'yes' as it's almost always a win.
# If you want to save some CPU in the saving child set it to 'no' but
# the dataset will likely be bigger if you have compressible values or keys.
rdbcompression yes

是否采用LZF压缩技术；

# Since version 5 of RDB a CRC64 checksum is placed at the end of the file.
# This makes the format more resistant to corruption but there is a performance
# hit to pay (around 10%) when saving and loading RDB files, so you can disable it
# for maximum performances.
#
# RDB files created with checksum disabled have a checksum of zero that will
# tell the loading code to skip the check.
rdbchecksum yes

RDB在版本5之后在文件末尾加入了CRC64校验和，这使得格式更抗损坏，但是在保存和加载RDB文件时，性能可能会受到影响(大约10%)，因此可以禁用它以获得最大性能；

数据库转储文件名

# The filename where to dump the DB
dbfilename dump.rdb

工作目录：

# The working directory.
#
# The DB will be written inside this directory, with the filename specified
# above using the 'dbfilename' configuration directive.
#
# The Append Only File will also be created inside this directory.
#
# Note that you must specify a directory here, not a file name.
dir ./

Redis快照设置：

1.保存到DB的方式；

2.是否采用LZF压缩技术；

3.数据库存储文件名；

4.数据文件存储文件夹；

Tips : 学习一个技术技巧

通用比较函数，支持比较结构体指定字段，支持Linux和Windows

#ifndef _WIN32
#define TYPEOF  typeof      // linux C98
#else
#define TYPEOF decltype     // windows C++11后支持
#endif

template <int offset, class TYPE>
bool CheckZero(const void* p)
{
    TYPE a = *(*TYPE)((char*)p + offset);
    return (bool)a;
}

template <int offset, typename T>
int CmpOneKey(const void *p1, const void *p2)
{
    T a1 = *(T*)((char*)p1 + offset);
    T a2 = *(T*)((char*)p2 + offset);

    if (a1 < a2)
        return -1;
    else if (a1 > a2)
        return 1;
    return 0;
}

template <int offset, typename T>
int DescCmpOneKey(const void* p1, const void* p2)
{
    return -CmpOneKey<offset, T>(p1, p2);
}

template <int offset1, typename T1, int offset2, typename T2>
int CmpTwoKey(const void* p1, const void* p2)
{
    int diff = CmpOneKey<offset1, T1>(p1, p2);
    if (diff == 0)
    {
        return CmpOneKey<offset2, T2>(p1, p2);
    }
    return diff;
}

template <int offset1, typename T1, int offset2, typename T2>
int DescCmpTwoKey(const void *p1, const void *p2)
{
    return -CmpTwoKey<offset1, T1, offset2, T2>(p1, p2);
}

template <int offset1, typename T1, int offset2, typename T2, int offset3, typename T3>
int CmpThreeKey(const void *p1, const void *p2)
{
    int diff = CmpTwoKey<offset1, T1, offset2, T2>(p1, p2);
    if (diff == 0)
    {
        return CmpOneKey<offset3, T3>(p1, p2);
    }
    return diff;
}

#define CHECK_ZERO(s, m) CheckZero<offsetof(s, m), TYPEOF(((s*)0)->m)>
#define CMP_ONE_KEY(s, m) CmpOneKey<offsetof(s, m), TYPEOF(((s*)0)->m)>
#define CMP_TWO_KEY(s, m1, m2) CmpTwoKey<offsetof(s, m1), TYPEOF(((s*)0)->m1, offsetof(s, m2), TYPEOF(((s*)0)->m2)>
#define CMP_THREE_KEY(s, m1, m2, m3) CmpThreeKey()<offsetof(s, m1), TYPEOF(((s*)0)->m1, offsetof(s, m2), TYPEOF(((s*)0)->m2), offsetof(s, m3), TYPEOF(((s*)0)->m3>
#define CMP_ONE_KEY_DESC(s, m) DescCmpOneKey<offsetof(s, m), TYPEOF(((s*)0)->m)>
#define CMP_TWO_KEY_DESC(s, m1, m2) DescCmpTwoKey<offsetof(s, m1), TYPEOF(((s*)0)->m1, offsetof(s, m2), TYPEOF(((s*)0)->m2)>

Share : 分享一篇有观点和思考的技术文章

TCP三次握手和SYN攻击:
原文链接：https://mp.weixin.qq.com/s?__biz=MzIwNTc4NTEwOQ==&mid=2247484888&idx=1&sn=aaf4f7f4a0b37c8f823e2665d711dd72&scene=21#wechat_redirect