## 5. Longest Palindromic Substring

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example 1:

Output: "bab"
Note: "aba" is also a valid answer.
Example 2:

Input: "cbbd"
Output: "bb"

``````/**
* @param {string} s
* @return {string}
*/
var longestPalindrome = function(s) {\
// palindromic str for single round
var o = "";
// Longest palindromic str
var max = "";
for (var i = 0; i < s.length; i ++){
var x = i;
var y = i;
// Include current char
o = s[i];

// Collect Same letters on the right
while(s[y+1] == s[y]){
y ++; i ++;
// append same char on the right to p_str
o += s[i];
}

// Then check both sides one by one
// Make sure x & y in range, then compare both ends
while(x > 0
&& y < s.length-1
&& s[x-1] == s[y+1]){
o = s[x-1] + o + s[y+1];
// Separate x & y for one more step
x--; y++;
}

// Save, if longer than current max record
if(o.length > max.length){
max = o;
}

}

return max;
};
``````

## 4. Median of Two Sorted Arrays

There are two sorted arrays nums1 and nums2 of size m and n respectively.

Find the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)).

You may assume nums1 and nums2 cannot be both empty.

Example 1:

nums1 = [1, 3]
nums2 = [2]

The median is 2.0
Example 2:

nums1 = [1, 2]
nums2 = [3, 4]

The median is (2 + 3)/2 = 2.5

``````
/**
* @param {number[]} nums1
* @param {number[]} nums2
* @return {number}
*/
var findMedianSortedArrays = function(nums1, nums2) {
// remove elements from both ends

while ((nums1.length + nums2.length)/2 > 1){
// If any of the arrays is empty, rm the other one
if(nums1.length == 0){
nums2.shift();
nums2.pop();
} else if(nums2.length == 0){
nums1.shift();
nums1.pop();
} else {
if(nums1[0] < nums2[0]){
nums1.shift();
} else {
nums2.shift();
}
// if nums1 is empty
//   OR nums1's tail is less than nums2's, remove nums2
if(nums1.length == 0 ||
nums1[nums1.length -1] < nums2[nums2.length -1]){
nums2.pop();
} else {
nums1.pop();
}
}
}
// only 1 or 2 elements remain now
var r = nums1.concat(nums2);
// send average for two
if(r.length > 1){
return (r[0]+r[1])/2;
} else {
// or just the last element
return r[0];
}
};
``````

## 3. Longest Substring Without Repeating

Given a string, find the length of the longest substring without repeating characters.

Example 1:

Input: "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.
Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.
Example 3:

Input: "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

``````/**
* @param {string} s
* @return {number}
*/
var lengthOfLongestSubstring = function(s) {
var max = 0;
var a = [];
for (var i = 0; i < s.length; i ++){
// If element exists, remove any other elements before it,
// and itself
if(a.includes(s[i])){
a.splice(0, a.indexOf(s[i]) + 1);
}
// Append new element
a.push(s[i]);
// Update result
if(max < a.length){
max = a.length;
}
}
return max;
};
``````

## Getting started with eBay API Tokens (Oauth) with PHP

Official Guide: http://developer.ebay.com/devzone/rest/ebay-rest/content/oauth-gen-user-token.html

I’ll also cover some mistakes I made.

1.  Signup at https://developer.ebay.com
2. Create an App and get the App ID (Client ID) and Cert ID (Client Secret)
3. Click ‘User Tokens‘ (either from sandbox or production, depend on you)
4. Click “Get a Token from eBay via Your Application” then “Add eBay Redirect URL
5. Fill in the form, the only important thing is the “Your auth accepted URL“, it should be under your domain. (You should able to extract the auth code from the call back later, for example \$_GET[‘code’] in PHP),  let’s assume this  https://yourdomain.com/accept.php
6. Take down the value of “RuName (eBay Redirect URL name)” and “Your branded eBay Production Sign In (OAuth)

So far, we’ve done our preparation at developer.ebay.com

Then, on you local developing environment or you production server,:

1. Set user login you own website
2. put a hyperlink pointing to the URL of “Your branded eBay Production Sign In (OAuth)
3. visitor click on that link, and login with their ebay account.
4. ebay will make a callback redirect to “Your auth accepted URL” if success.

On the “Your auth accepted URL“, prepare a PHP script that get the value of \$_GET[‘code’] and save it in sessions. It starts with ‘v%5E1’. this is called “Authorization Code

Next, get an “Access Token” with this “Authorization Code”

Craft a HTTP Request with whatever you like with PHP.

Content-Type = application/x-www-form-urlencoded
Authorization = Basic <B64-encoded-oauth-credentials>

HTTP method: POST

URL: https://api.sandbox.ebay.com/identity/v1/oauth2/token

Request body (wrapped for readability):
grant_type=authorization_code&
code=<authorization-code-value>&
redirect_uri=<redirect_URI>

We have three ‘Variables’ here.

<B64-encoded-oauth-credentials>: Use a Chrome Browser, Right click, Inspect, Console
Then type: btoa(‘APP_ID:CERT_ID‘);
We did take down these two values earlier. and there is a : between.
Hit ENTER, the value inside the double quotes is <B64-encoded-oauth-credentials>

<authorization-code>: the ‘Authorization Code‘ we got in the callback redirect.

<redirect_URI>: This is the tricky part. This can’t be ignored or filled with random things, it’s the value of “RuName (eBay Redirect URL name)

Send the request, and you’ll get the access token and the refresh token.
Follow the official guide to refresh the token if expired.

We are basically finished here, If you wanna call an API, ‘List orders as a seller’ for instance:

GET https://api.ebay.com/sell/fulfillment/v1/order

Authorization: Bearer <YOUR_ACCESS_TOKEN>
It’s Bearer this time :), don’t use Basic by mistake.

## Remove the Loop Icon for VOX

VOX is the best music players on OSX I’ve ever used.

The Loop becomes one of it’s features to store unlimited music on it’s platform. It’s a good feature, and the only way for the developer to get some pay back for the wonderful applet.

I just don’t need it, and try to save some space for my menu bar.

On the VOX’s preference page, uncheck “Keep Loop Agent Running when” just doesn’t make any sense. Neither for “launchctl remove com.coppertino.VOXCloud” as the developer mentioned.

My way to close that:

Finder – Application – VOX – right click – Show package contents – Contents – Library – LoginItems

You can find the Loop.app here, but things like deleting/renaming/[removing permission] will all prevent VOX from launching.

Loop.app – Show package contents – Contents – Resources – Base.lproj

Then rename “MainMenu.nib” to something else for example: “MainMenu.nib.bye”

Quit Loop and restart VOX, Done.

## Important:

Double check your operate system: ONLY  Debian 8 (Jessie) works with this instruction

Apache version: 2.4 which is the default version comes with Debian 8 (Not working with Apache 2.2 or lower)

## Install Apache2:

Update package list and upgrade outdated packages:

`sudo apt-get update && sudo apt-get upgrade`

Install Apache2:

`sudo apt-get install apache2`

## Install PHP7:

Since PHP7 is not included in any Debian official source list, we gonna use the version compiled by Dotdeb.org, which is pretty widely used.

`sudo nano /etc/apt/sources.list`

Add the following two lines to the end of the file:

```deb http://packages.dotdeb.org jessie all
deb-src http://packages.dotdeb.org jessie all```

If you server is far from US, try find the nearest mirror: https://www.dotdeb.org/mirrors/

Get and Install GnuPG key:

```wget https://www.dotdeb.org/dotdeb.gpg
sudo apt-key add dotdeb.gpg```

Update packages again

`sudo apt-get update`

Install PHP7:

here is a list of available packages currently: (By the way, Swoole also work with php7, use ‘pecl install swoole to install’)

```php7.0-apcu       php7.0-dbg        php7.0-imagick    php7.0-memcached  php7.0-phpdbg     php7.0-sybase
php7.0-apcu-bc    php7.0-dev        php7.0-imap       php7.0-mongodb    php7.0-pspell     php7.0-tidy
php7.0-bz2        php7.0-enchant    php7.0-interbase  php7.0-msgpack    php7.0-readline   php7.0-xdebug
php7.0-cgi        php7.0-fpm        php7.0-intl       php7.0-mysql      php7.0-recode     php7.0-xmlrpc
php7.0-cli        php7.0-gd         php7.0-json       php7.0-odbc       php7.0-redis      php7.0-xsl
php7.0-common     php7.0-gmp        php7.0-ldap       php7.0-opcache    php7.0-snmp
php7.0-curl       php7.0-igbinary   php7.0-mcrypt     php7.0-pgsql      php7.0-sqlite3
```

Choose your list of mod, install with php

`sudo apt-get install php7.0 php7.0-common php-pear #add your list of mods here`

Install mod_php7 for Apache 2.4 and restart apache:

```sudo apt-get install libapache2-mod-php7.0
sudo service apache2 restart```

That’s it! Done!

## What’s sshd_config?

It’s “OpenSSH SSH daemon configuration file”

Simply means the config file for OpenSSH Server.

Located at /etc/ssh/sshd_config

## My reference

http://www.freebsd.org/cgi/man.cgi?query=sshd_config

## ListenAddress and Port

By default, OpenSSH will listen on port 22 for all address(0.0.0.0 and ::)

There can be multiple Port defined, for example:

```Port 22
Port 622
```

OpenSSH will listen on both ports

ListenAddress specify the address to listen, the address can be hostname, ipv4 or ipv6

You may also add an optional port number, for example:

```ListenAddress 192.168.1.120
```

OpenSSH will listen on 192.168.1.120 and ddns.example.com at port 22, plus 1.2.3.4 port 922

If there are multiple “Port” specified:

```Port 22
Port 622
```

Then 192.168.1.120:22   192.168.1.120:622   1.2.3.4:922  ddns.example.com:22  ddns.example.com:622 are listened

If port is not specified, sshd will listen on the address and all prior Port options specified.

## Access Control:

Process order: DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups.

If none of the four is defined, login is allowed fro all users.

If Allow* is defined, login is only allowed to declared users and groups.

Only username and groupname are accepted, UID and GID are NOT.

In the following example, only ‘root’ and ‘user’ are allowed

```PermitRootLogin yes
AllowUsers root user```

In the following example, only ‘user2’ is denied.

`DenyUsers user2`

## Limit user to specified destination address and port

Supposed the OpenSSH server is listening to multiple IPs (1.1.1.1 and 2.2.2.2)

At the end of sshd_config file: add:

```# Only user'git' can access to server address 2.2.2.2
AllowUsers git```

You may also specify port

```# Only user'git' can access to server at port 622
Match LocalPort 622
AllowUsers git```

You may also specify address and port

```# Only user'git' can access to server 2.2.2.2:622
Match LocalAddress 2.2.2.2 LocalPort 622
AllowUsers git
```

Note:

Match Introduces a conditional block. If all of the criteria on the Match line are satisfied, the keywords on the following lines override those set in the global section of the config file, until either another Match line or the end of the file. If a keyword appears in multiple Match blocks that are satisfied, only the first instance of the keyword is applied.

## Limit user from specified source address

```# Allow root only from client_ddns.example.com and Allow 'user from' 67.67.67.0/24
# Allow user2 from any host
AllowUsers [email protected]_ddns.example.com [email protected]* user2```

More details on HOST:

Host: Restricts the following declarations (up to the next Host or Match keyword) to be only for those hosts that match one of the patterns given after the keyword. If more than one pattern is provided, they should be separated by whitespace. A single `*' as a pattern can be used to provide global defaults for all hosts. The host is the hostname argument given on the command line (i.e. the name is not converted to a canonicalized host name before matching). A pattern entry may be negated by prefixing it with an exclama- tion mark (`!’). If a negated entry is matched, then the Host entry is ignored, regardless of whether any other patterns on the line match. Negated matches are therefore useful to provide exceptions for wildcard matches.

### Here is another approach using Match:

At the end of sshd_config file: add:

```# Only user'git' can access to server address 2.2.2.2
Match Address 67.67.67.0/24 User user
AllowUsers user```

## Bugs and Tips found recently

1: Teensy as a keyboard does not work properly in GRUB.

Solution: break your long input into parts (<=3 chars) and add delays (50ms is enough) between them.

2: In Debian and Ubuntu, your may install some PHP PECL modules just by using

`sudo apt-get install php5-pecl-http php5-propro php5-raphf`

(PHP run as an apache mod)

Restart Apache, php -m does not show any new module installed.

Try add ini files(propro.ini File Content: extension=propro.so) to /etc/php5/mod-available and make link (15-propro.ini for example) at /etc/php5/apache/conf.d pointing to /etc/php5/mod-available/propro.ini

restart Apache again, php module still not loading.

The solution:

use php5enmod propro instead :)
3: Dell PowerEdge RAID Controller (PERC) H730 and SSD.
Unable to build raid for Samsung 850 EVO SSD in the Lifecycle Manager.

Solution: goto BIOS and find device management- raid controller then build your RAID there.