Jason Fung Blog

Merge sort for inversion

2012-06-19T00:06:00.001+10:00

To calculate the inversion, here provided with two functions to do it.

First one is brute force. This is easy for everyone to understand, however, this will take long time especially for a large input.

Following is the code for brute-force method to get the inversion of an array list:

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To perform better, we can use merge-sort to implement this, at the step of "merge", we need to add one line code for count inversion.

Following is the code for merge-sort to get the inversion of an array list:

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MySQL Field Types

2012-06-13T10:49:00.002+10:00

MySQL Field Types

MySQL supports a number of column types, which may be grouped into three categories: numeric types, date and time types, and string (character) types. This section first gives an overview of the types available. Please refer to the MySQL manuals for more details.

Type	Use for	Size
TINYINT	A very small integer	The signed range is –128 to 127. The unsigned range is 0 to 255.
SMALLINT	A small integer	The signed range is –32768 to 32767. The unsigned range is 0 to 65535
MEDIUMINT	A medium-size integer	The signed range is –8388608 to 8388607. The unsigned range is 0 to 16777215
INT or INTEGER	A normal-size integer	The signed range is –2147483648 to 2147483647. The unsigned range is 0 to 4294967295
BIGINT	A large integer	The signed range is –9223372036854775808 to 9223372036854775807. The unsigned range is 0 to 18446744073709551615
FLOAT	A small (single-precision) floating-point number. Cannot be unsigned	Ranges are –3.402823466E+38 to –1.175494351E-38, 0 and 1.175494351E-38 to 3.402823466E+38. If the number of Decimals is not set or <= 24 it is a single-precision floating point number
DOUBLE, DOUBLE PRECISION, REAL	A normal-size (double-precision) floating-point number. Cannot be unsigned	Ranges are -1.7976931348623157E+308 to -2.2250738585072014E-308, 0 and 2.2250738585072014E-308 to 1.7976931348623157E+308. If the number of Decimals is not set or 25 <= Decimals <= 53 stands for a double-precision floating point number
DECIMAL, NUMERIC	An unpacked floating-point number. Cannot be unsigned	Behaves like a CHAR column: “unpacked” means the number is stored as a string, using one character for each digit of the value. The decimal point, and, for negative numbers, the ‘-‘ sign is not counted in Length. If Decimals is 0, values will have no decimal point or fractional part. The maximum range of DECIMAL values is the same as for DOUBLE, but the actual range for a given DECIMAL column may be constrained by the choice of Length and Decimals. If Decimals is left out it’s set to 0. If Length is left out it’s set to 10. Note that in MySQL 3.22 the Length includes the sign and the decimal point
DATE	A date	The supported range is ‘1000-01-01’ to ‘9999-12-31’. MySQL displays DATE values in ‘YYYY-MM-DD’ format
DATETIME	A date and time combination	The supported range is ‘1000-01-01 00:00:00’ to ‘9999-12-31 23:59:59’. MySQL displays DATETIME values in ‘YYYY-MM-DD HH:MM:SS’ format
TIMESTAMP	A timestamp	The range is ‘1970-01-01 00:00:00’ to sometime in the year 2037. MySQL displays TIMESTAMP values in YYYYMMDDHHMMSS, YYMMDDHHMMSS, YYYYMMDD or YYMMDD format, depending on whether M is 14 (or missing), 12, 8 or 6, but allows you to assign values to TIMESTAMP columns using either strings or numbers. A TIMESTAMP column is useful for recording the date and time of an INSERT or UPDATE operation because it is automatically set to the date and time of the most recent operation if you don’t give it a value yourself
TIME	A time	The range is ‘-838:59:59’ to ‘838:59:59’. MySQL displays TIME values in ‘HH:MM:SS’ format, but allows you to assign values to TIME columns using either strings or numbers
YEAR	A year in 2- or 4- digit formats (default is 4-digit)	The allowable values are 1901 to 2155, and 0000 in the 4 year format and 1970-2069 if you use the 2 digit format (70-69). MySQL displays YEAR values in YYYY format, but allows you to assign values to YEAR columns using either strings or numbers. (The YEAR type is new in MySQL 3.22.)
CHAR	A fixed-length string that is always right-padded with spaces to the specified length when stored	The range of Length is 1 to 255 characters. Trailing spaces are removed when the value is retrieved. CHAR values are sorted and compared in case-insensitive fashion according to the default character set unless the BINARY keyword is given
VARCHAR	A variable-length string. Note: Trailing spaces are removed when the value is stored (this differs from the ANSI SQL specification)	The range of Length is 1 to 255 characters. VARCHAR values are sorted and compared in case-insensitive fashion unless the BINARY keyword is given
TINYBLOB, TINYTEXT		A BLOB or TEXT column with a maximum length of 255 (2^8 - 1) characters
BLOB, TEXT		A BLOB or TEXT column with a maximum length of 65535 (2^16 - 1) characters
MEDIUMBLOB, MEDIUMTEXT		A BLOB or TEXT column with a maximum length of 16777215 (2^24 - 1) characters
LONGBLOB, LONGTEXT		A BLOB or TEXT column with a maximum length of 4294967295 (2^32 - 1) characters
ENUM	An enumeration	A string object that can have only one value, chosen from the list of values ‘value1’, ‘value2’, ..., or NULL. An ENUM can have a maximum of 65535 distinct values.
SET	A set	A string object that can have zero or more values, each of which must be chosen from the list of values ‘value1’, ‘value2’, ... A SET can have a maximum of 64 members

The letter analogy for REST vs. SOAP

2012-01-07T11:41:00.002+11:00

A nice analogy for REST vs. SOAP is mailing a letter: with SOAP, you're using an envelope; with REST, it's a postcard. Postcards are easier to handle (by the receiver), waste less paper (i.e., consume less bandwidth), and have a short content. (Of course, REST requests aren't really limited in length, esp. if they use POST rather than GET.)

But don't carry the analogy too far: unlike letters-vs.-postcards, REST is every bit as secure as SOAP. In particular, REST can be carried over secure sockets (using the HTTPS protocol), and content can be encrypted using any mechanism you see fit. Without encryption, REST and SOAP are both insecure; with proper encryption in place, both are equally secure.

How to restart network in Linux

2011-12-22T17:27:00.000+11:00

RedHat:

# service network restart
or
# /etc/init.d/network restart

# service network start

# service network stop

Debian:

# /etc/init.d/networking restart

# /etc/init.d/networking start

# /etc/init.d/networking stop

Ubuntu:

# sudo /etc/init.d/networking restart

# sudo /etc/init.d/networking start

# sudo /etc/init.d/networking stop

Software Testing List

2011-12-20T12:24:00.004+11:00

Just try to list all kind of software testing here.

White box testing – (also known as clear box testing, glass box testing, transparent box testing, and structural testing) is a method of testing software that tests internal structures or workings of an application, as opposed to its functionality (i.e. black-box testing). In white-box testing an internal perspective of the system, as well as programming skills, are required and used to design test cases. The tester chooses inputs to exercise paths through the code and determine the appropriate outputs. This is analogous to testing nodes in a circuit, e.g. in-circuit testing (ICT).While white-box testing can be applied at the unit, integration and system levels of the software testing process, it is usually done at the unit level. It can test paths within a unit, paths between units during integration, and between subsystems during a system level test. Though this method of test design can uncover many errors or problems, it might not detect unimplemented parts of the specification or missing requirements.

Black box testing – is a method of software testing that tests the functionality of an application as opposed to its internal structures or workings (see white-box testing). Specific knowledge of the application's code/internal structure and programming knowledge in general is not required. The tester is only aware of what the software is supposed to do, but not how i.e. when he enters a certain input, he gets a certain output; without being aware of how the output was produced in the first place[1]. Test cases are built around specifications and requirements, i.e., what the application is supposed to do. It uses external descriptions of the software, including specifications, requirements, and designs to derive test cases. These tests can be functional or non-functional, though usually functional. The test designer selects valid and invalid inputs and determines the correct output. There is no knowledge of the test object's internal structure.

Unit testing – is a method by which individual units of source code are tested to determine if they are fit for use. A unit is the smallest testable part of an application. In procedural programming a unit could be an entire module but is more commonly an individual function or procedure. In object-oriented programming a unit is often an entire interface, such as a class, but could be an individual method.[citation needed] Unit tests are created by programmers or occasionally by white box testers during the development process.
Ideally, each test case is independent from the others: substitutes like method stubs, mock objects, fakes and test harnesses can be used to assist testing a module in isolation. Unit tests are typically written and run by software developers to ensure that code meets its design and behaves as intended. Its implementation can vary from being very manual (pencil and paper) to being formalized as part of build automation.

Integration testing – Testing of integrated modules to verify combined functionality after integration. Modules are typically code modules, individual applications, client and server applications on a network, etc. This type of testing is especially relevant to client/server and distributed systems.

Incremental integration testing – Bottom up approach for testing i.e continuous testing of an application as new functionality is added; Application functionality and modules should be independent enough to test separately. done by programmers or by testers.

Functional testing – is a type of black box testing that bases its test cases on the specifications of the software component under test. Functions are tested by feeding them input and examining the output, and internal program structure is rarely considered (Not like in white-box testing).

System testing – is testing conducted on a complete, integrated system to evaluate the system's compliance with its specified requirements. System testing falls within the scope of black box testing, and as such, should require no knowledge of the inner design of the code or logic.

End-to-end testing – Similar to system testing, involves testing of a complete application environment in a situation that mimics real-world use, such as interacting with a database, using network communications, or interacting with other hardware, applications, or systems if appropriate.

Sanity testing - Testing to determine if a new software version is performing well enough to accept it for a major testing effort. If application is crashing for initial use then system is not stable enough for further testing and build or application is assigned to fix.

Regression testing – is any type of software testing that seeks to uncover new errors, or regressions, in existing functionality after changes have been made to a system, such as functional enhancements, patches or configuration changes.The intent of regression testing is to ensure that a change, such as a bugfix, did not introduce new faults. "One of the main reasons for regression testing is that it's often extremely difficult for a programmer to figure out how a change in one part of the software will echo in other parts of the software."

Acceptance testing - is a test conducted to determine if the requirements of a specification or contract are met. User or customer do this testing to determine whether to accept application.

Load testing – is the process of putting demand on a system or device and measuring its response. Load testing is performed to determine a system’s behavior under both normal and anticipated peak load conditions. It helps to identify the maximum operating capacity of an application as well as any bottlenecks and determine which element is causing degradation. When the load placed on the system is raised beyond normal usage patterns, in order to test the system's response at unusually high or peak loads, it is known as stress testing. The load is usually so great that error conditions are the expected result, although no clear boundary exists when an activity ceases to be a load test and becomes a stress test.

Performance testing – is used to determine the speed or effectiveness of a computer, network, software program or device. This process can involve quantitative tests done in a lab, such as measuring the response time or the number of MIPS (millions of instructions per second) at which a system functions. Qualitative attributes such as reliability, scalability and interoperability may also be evaluated. Performance testing is often done in conjunction with stress testing.

Usability testing – User-friendliness check. Application flow is tested, Can new user understand the application easily, Proper help documented whenever user stuck at any point. Basically system navigation is checked in this testing.

Install/uninstall testing – Tested for full, partial, or upgrade install/uninstall processes on different operating systems under different hardware, software environment.

Recovery testing – is the activity of testing how well an application is able to recover from crashes, hardware failures and other similar problems. Recovery testing is the forced failure of the software in a variety of ways to verify that recovery is properly performed. Recovery testing should not be confused with reliability testing, which tries to discover the specific point at which failure occurs.Recovery testing is basically done in order to check how fast and better the application can recover against any type of crash or hardware failure etc. Type or extent of recovery is specified in the requirement specifications. It is basically testing how well a system recovers from crashes, hardware failures, or other catastrophic problems

Security testing – is a process to determine that an information system protects data and maintains functionality as intended. The six basic security concepts that need to be covered by security testing are: confidentiality, integrity, authentication, availability, authorization and non-repudiation. Security testing as a term has a number of different meanings and can be completed in a number of different ways. As such a Security Taxonomy helps us to understand these different approaches and meanings by providing a base level to work from.

Compatibility testing – Testing how well software performs in a particular hardware/software/operating system/network environment and different combinations of above.

Comparison testing – Comparison of product strengths and weaknesses with previous versions or other similar products.

Alpha testing – is simulated or actual operational testing by potential users/customers or an independent test team at the developers' site. Alpha testing is often employed for off-the-shelf software as a form of internal acceptance testing, before the software goes to beta testing.

Beta testing – comes after alpha testing and can be considered a form of external user acceptance testing. Versions of the software, known as beta versions, are released to a limited audience outside of the programming team. The software is released to groups of people so that further testing can ensure the product has few faults or bugs. Sometimes, beta versions are made available to the open public to increase the feedback field to a maximal number of future users.

Reference:http://en.wikipedia.org, http://www.softwaretestinghelp.com

How To Install Alternate Keyboard Apps On Kindle Fire

2011-12-07T10:41:00.001+11:00

There are lots of tutorial flying around about how to install alternate keyboard on Kindle, but most of them need to connect Kindle Fire to PC/MAC/Linux with typing commands, this may not easy for some ppl.

So, here I will show you an easier way to install it on your Kindle Fire.

Pre-request:

Your Kindle is rooted. If not, see this link

Installed Root Explorer app.

Now, let's start:

1. Install the keyboard you want as normal, for example Swiftkey X Keyboard.(You can install directly from Android Market or install manually by transfer the apk file to Kindle Fire.)

2. Open Root Explorer, go to /data/app, the keyboard you just installed should have a apk file here. Move it to /system/app, remember it is move, not copy.

3. Reboot your Kindle Fire.

4. Open Root Explorer again, go to /system/app, you can see the apk file you just moved at step 2. Click it and install it, after finished install, DELETE the apk file. Yes, delete it.

5. DONE!

Leave any comments if you got problems with this.

How to root your Kindle Fire in Mac or Linux

2011-12-02T10:20:00.001+11:00

There are lots of tutorial on internet talk about how to root kindle fire in Windows. But hey, remember, most of the geeks are using Mac or Linux. So, Here is a tutorial for root your Kindle Fire in Mac or Linux.

First of all, some preparations:

In your Kindle Fire, Go to Setting -> More -> Device and make sure the “Allow Installation of Applications” is checked “ON” (ON is yellow).
Download the KindleFireRootMacLinux.zip, upzip to anywhere you feel comfortable with.

OK, you got all you need.

Now, connect you Kindle Fire with you computer vis micro USB cable. After connected, click "Disconnect" on Kindle Fire to turn off the USB disk drive mode.

Let's start with terminal:

Go to the KindleFireRootMacLinux directory by type cd your/path/to/KindleFireRootMacLinux
Create a new directory by type mkdir ~/.android
Copy file to the newly created directory by type cp adb_usb.ini ~/.android/.
Verify your Kindle Fire is recognized by you computer by type

In Mac: ./adb-mac kill-server
./adb-mac devices
In Linux: ./adb-linux kill-server
./adb-linux devices
If you can see sort of like below (the number is just an example),
List of device attached
3491283482323000000001 device
That means you are good to go with one more step to root you Kindle Fire.

Here is the last step:

TYPE: sh runmemac.sh in Mac
or
sh runmelinux.sh in Linux

Now, your Kindle Fire do its rooting and reboot.
After you Kindle Fire reboot, you can verify it by go to Settings->More->Applications->All Applications, then you should see SuperUser app.

Congrats! DONE!!!

Leave any comments if you got problems with this.

For install Android Market on your Kindle Fire, please refer to this link.

How to change password in Linux

2011-11-30T14:18:00.001+11:00

To change your password:
$ passwd

To change "tom" password:
$ passwd tom

How to open a port in Redhat / Fedora Linux

2011-11-30T14:02:00.001+11:00

Open flle /etc/sysconfig/iptables:
# vi /etc/sysconfig/iptables

then append the following rule:
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 8080 -j ACCEPT

then the last step is to restart iptables:
# /etc/init.d/iptables restart

How to set up Nexus with your Maven

2011-11-17T16:47:00.001+11:00

This is step-by-step instruction to set up nexus on Linux/Mac to work integrated with maven.

Fist of all, install nexus.

1. Download nexus at http://nexus.sonatype.org/downloads/ , the file name should be like nexus-oss-webapp-1.9.X.X-bundle.tar.gz.

2. Save the file to /usr/local or in terminal type: sudo mv nexus-oss-webapp-1.9.X.X-bundle.tar.gz /usr/local/

3. Go to directory by type: cd /usr/local, then untar the file: tar -xvzf nexus-oss-webapp-1.9.X.X-bundle.tar.gz then link the directory with name "nexus" : ln -s nexus-oss-webapp-1.9.X.X nexus

Then, start nexus.

4. Go to the newly created nexus directory: cd /usr/local/nexus

5. Show all the supported OS platform: ls ./bin/jsw/

6. Change the file access: chmod -R a+x bin

7. Start nexus with specific platform name in the command: ./bin/jsw/{platform- name}/nexus start

8.Check the log to verify: tail -f logs/wrapper.log

(The lof should contains SelectChannelConnector@0.0.0.0:8081)

9. To verify in the browser, open chrome, type in URL http://localhost:8081/nexus, on the right top should be clickable login, click and login with default username:admin and password:admin123.

To config your maven in your local machine to use the nexus as the repository, you need to change the seeting.xml in maven conf directory, to so this, use any editor open mavan_home/conf/setting.xml, add the following lines before the </settings>

<mirrors>

<mirror>

<id>nexus</id>

<mirrorOf>*</mirrorOf>

<url>http://107.20.245.79:8081/nexus/content/groups/public</url>

</mirror>

</mirrors>

<profiles>

<profile>

<id>nexus</id>





<repositories>

<repository>

<id>central</id>

<url>http://central</url>

<releases><enabled>true</enabled></releases>

<snapshots><enabled>true</enabled></snapshots>

</repository>

</repositories>

<pluginRepositories>

<pluginRepository>

How to disable cursor blinking in GNOME

2011-11-14T10:23:00.001+11:00

GNOME used to provided a special option in the terminal menu, however with the latest version, this option is gone. So, in order to disable cursor blinking, all we need to do is to disable by command line as following:

gconftool-2 -s /apps/gnome-terminal/profiles/Default/cursor_blink_mode -t string off

Handy bash commands

2011-11-09T16:58:00.003+11:00

Handy bash commands for finding out stuff in Linux:
# Find CPU specifications
cat /proc/cpuinfo

# Find running kernel version
uname -r

# What compiler version do I have installed
gcc -v
gcc --version

# What is the running kernel and compiler installed
cat /proc/version

# Find X server version
X -showconfig

# What pci cards are installed and what irq/port is used
cat /proc/pci

# What kernel modules are loaded
lsmod

# Memory and swap information
cat /proc/meminfo

# How are the hard drives partitioned
fdisk -l

# How much free/used drive space
df -h

# Show disk usage by current directory and all subdirectories
du | less

# What takes up so much space on your box
# Run from the directory in question and the largest chunk shows up last
find $1 -type d | xargs du -sm | sort -g

# What is the distribution
cat /etc/.product
cat /etc/.issue
cat /etc/issue
cat /etc/issue.net
sysinfo

# For finding or locating files
find
locate
which
whereis

# Use dmesg to view the kernel ring buffer (error messages)
dmesg | less

# Watch error messages as they happen (sysklog needed)
as root, tail -f /var/log/messages (shows last 10 lines, use a number in front of f for more lines)

# What processes are running
ps -A

# Find a process by name
ps -ef | grep -i
For example, XCDroast
ps -ef xcdroast

# See current environment list, or pipe to file
env | more
env > environmentvariablelist.txt

# Show current userid and assigned groups
id

# See all command aliases for the current user
alias

# See rpms installed on current system
rpmquery --all | less
rpmquery --all >
rpmquery --all | grep -i