JavaScript Style Guide Study - Airbnb

August 17, 2016

Plan to spend 3+ hours to go over the JavaScript Style Guide. 

1. Airbnb JavaScript Style Guide()  - English Version 

https://github.com/airbnb/javascript

2. Airbnb JavaScript Style Guide() - Chinese version

https://github.com/yuche/javascript#table-of-contents

36 Topics

Types
References
Objects
Arrays
Destructuring

Strings
Functions
Arrow Functions
Classes & Constructors
Modules


Iterators and Generators (NO. 11)
Properties
Variables
Hoisting
comparison Operators & Equality

Blocks
Comments
Whitespace
commas
Semicolons


Type Casting & Coercion (No. 21)
Naming Conventions
Accessors
Events
jQuery

ECMAScript 5 Compatibility
ECMAScript 6 Styles
Testing
Performance
Resources


In the Wild
Translation
The JavaScript Style Guide Guide
Chat With Us about JavaScript
Contributors
License

Reading while going through JavaScript style guide from Airbnb:

1. JavaScript spread syntax...  - 10 minutes

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Spread_operator


2. Read JavaScript Array.From - 20 minutes

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/from

3. Destructuring assignment  10 minutes

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment


4. Template literals - 10 minutes reading

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Template_literals

new terms: back-tick(``), neither double nor single quotes


5. Default parameters -
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Template_literals

Editorial notes:
1. Write down all new terms in the guide. Understand the terms.
2. Try to memorize all the guide. Design some drills to help.
3. Invest time first to read the good style code, and then, start to write more JavaScript code.
4. Focus on the document, understand why? What to avoid? Good or bad or Excellent idea?

Favorite blogs of day:
web front technologies 
1. https://github.com/qiu-deqing/FE-learning

Leetcode 380 - Insert, delete, getRandom() O(1) time - Practice 4

August 16, 2016

The first 3 practices:


http://juliachencoding.blogspot.ca/2016/08/leetcode-380-insert-delete-getrandom-o1.html

http://juliachencoding.blogspot.ca/2016/08/leetcode-380-insert-delete-getrandom-o1_16.html

http://juliachencoding.blogspot.ca/2016/08/leetcode-380-insert-delete-getrandom-o1_89.html

Read the blog:
http://www.guoting.org/leetcode/leetcode-380-insert-delete-getrandom-o1/

Java code from the above blog:
https://gist.github.com/jianminchen/9561828feda21bac20bc9ba4da0d13c8

4th practice using C#:

https://gist.github.com/jianminchen/7741fabf57413ccbb1080f6f691bb532

Highlights of 4th practice:

1. Thinking problem solving using an array:

 Insertion of array is to append the number at the end of array, O(1);

 Delete a number from the array, for example, at index position i of array with length n, then, all elements from i+1 to n-1 should be shifted to left one position - time complexity is O(n-i) = O(n)

 getRandom() - time complexity is O(1), just get a random number r from 0 to n, and then, return arr[r].
   Array value can be any integer number, and in the range of Int32.min - Int32.max, so given an integer value, it may not be in the array; if it is, to find the index of array to hold the value, we need to look up a hashmap with value/ index of array pair first. 

So, in order to make it O(1) for the deletion, we can use extra space to speed up time to O(1). The idea is to move last number in the array to the position of deleted element.

Extra space - a hashmap to store each number in the array as key, and the value is the position in the array.

4. Introduce new design in the practice? 

arrayDeletionO1 - line 150 API - array deletion, arrayDeletionO1 (Dictionary<Int32, Int32> arr, Dictionary<Int32, Int32> map, int val)

- implement the array deletion in time complexity O(1)

move - line 173 API - array move - move an entry from the dictionary from one location to another location. move(Dictionary<Int32, Int32> dict, int from, int to)

mapUpdateForArrayDeletion - line 129 - hashmap update - mapUpdateForArrayDeletion(Dictionary<Int32, Int32> arr, Dictionary<Int32, Int32> map, int val)

Cons and pros for modified deletion for the array-like data structure:
1. Cons: If the array is sorted, then the order is lost. No longer in the order.
2. Study Array API for C, C++, C#, JavaScript, none of them has API like this. Why?

Array - JavaScript
http://juliachencoding.blogspot.ca/2016/07/javascript-array-mozilla-60-minutes.html

C# array
http://juliachencoding.blogspot.ca/2016/06/array-class-c-c-javascript-java.html

3. For the deletion, update can be done directly instead of first deletion, and then move of the last one to the deleted item's position. line 182, line 183 can be merged to one line - update.

4th practice using C#:
https://gist.github.com/jianminchen/7741fabf57413ccbb1080f6f691bb532

4. JavaScript array is sparse, the array is not contiguous. For Leetcode 380, Julia thought about array deletion design, if the array is leaving as sparse after deletion, then, getRandom() can not be O(1). If the sparse slot is selected by random algorithm, need to select another one.

Related articles:
 1. Uber map article:
http://goo.gl/nmRv18

Google search keyword:
red-black tree - C++ implements the map
http://stackoverflow.com/questions/5288320/why-is-stdmap-implemented-as-a-red-black-tree

2. Uber algorithm question: 
https://goo.gl/fWq132

Leetcode 380 - Insert, delete, getRandom() O(1) time - Practice 3

August 16, 2016

After first 2 practices, Julia read the blog:
http://www.guoting.org/leetcode/leetcode-380-insert-delete-getrandom-o1/


3rd practice using C#:

https://gist.github.com/jianminchen/9a8aef6220d285aac3f22abac984e0b3

Leetcode 380 - Insert, delete, getRandom() O(1) time - Practice 2

August 16, 2016

 First practice on Leetcode 380:

http://juliachencoding.blogspot.ca/2016/08/leetcode-380-insert-delete-getrandom-o1.html

 Add one more function - design API - Julia likes to design API, after she tried to memorize all APIs of JavaScript array.

Second practice - one function:

https://gist.github.com/jianminchen/84a0945eb49d3ae7af36b4ca5f0f0c41

Design API - move an entry from the dictionary from one location

to another location

assume that dictionary contains the entry of from

assume that to position is available in the dictionary

public bool move(Dictionary<Int32, Int32> dict, int from, int to)

Blog:
1. CSS style -
http://codeguide.bootcss.com/

2. http://www.ruanyifeng.com/blog/2012/10/javascript_module.html

Leetcode 380 - Insert, delete, getRandom() O(1) time - Practice 1

August 8, 2016

Problem statement:

Design a data structure that supports all following operations in average O(1) time.

1. insert(val): Inserts an item val to the set if not already present.
2. remove(val): Removes an item val from the set if present.
3. getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.

Go over the website Java code, write a C# version: 

http://www.programcreek.com/2014/08/leetcode-insert-delete-getrandom-o1-java/

Java code from the above webpage:
https://gist.github.com/jianminchen/b6ab09a8a047db42da4ad663036d621a

C# code written by Julia
https://gist.github.com/jianminchen/9ebfbe7462c17689344578be31c804c0

Highlights of practice:

1. Spent 20+ minutes to write the function remove(int val)
2. Put test cases into main function, test the code to understand the problem.
3. Did not understand the design, why two hashmaps are used.
4. Concern about function remove - line 133 - 165
    The function is not readable - one function does so many things - break Single Responsibility Principle.

Microsoft Development Service - watch and learn

August 14, 2016

 Great time to watch and learn. First thing in the Sunday morning is to relax and learn.

Blogs to read:
http://stories.visualstudio.com/bing-continuous-delivery/

Videos:

1. Full Keynote: The Future of Microsoft Tools and Services for the New Role of Developers
https://www.youtube.com/watch?v=Gks7Ngzt5Yw

2. Keynote: Visual Studio 2015 - Any App, Any Developer
https://www.youtube.com/watch?v=Nj1luMpj7mI

Blogs to read:

1. Leetcode 380: (code study: Leetcode blogs)
http://www.guoting.org/leetcode/leetcode-380-insert-delete-getrandom-o1/

2. Leetcode 380 - Insert Delete GetRandom O(1)
https://leetcode.com/problems/insert-delete-getrandom-o1/

3. Read the article
http://www.programcreek.com/2014/08/leetcode-insert-delete-getrandom-o1-java/

4. Read Uber map article:
http://goo.gl/nmRv18

Google search keyword:
red-black tree - C++ implements the map

2.
https://goo.gl/fWq132

Clip: cropping an image - CSS learning and sharing on JSFiddle

August 12, 2016

Clip is the CSS feature to clip an image using scripts. Julia spent more than one hour to work on a few lines of CSS code, and then, she chose to use a specific image to help.

If you have an image with 500px x 500px, you may like to get one small image with size 100px x 100px without using Microsoft paint to cut and save as a new file. The solution is to use CSS clip.

Basics to find out the solution:
CSS:
1. position relative/ absolute
2. rect
3. clip
4. an example to explain how to put together
5. play with Firefox firebug, and then figure out CSS settings.

Study the article:
http://www.xul.fr/en/css/clip.php

Spent more than 1 hour to figure out how to set up .clipzone width and height. There are a few ways to set up CSS, but she likes to write down her tips to solve the problem.

After more than one hour confusion, she decided to customize an image with some grids and text, with size of 500px x 500px, see the following:

With a few mistakes, she figured out how to configure them quickly. Let us talk about a problem, and then, solve the problem using CSS clip property based on the article (ref. 2).

Problem statement:
How to clip the image 100px x 100px in the center of the above image, with text 13?

Here is the image: 

The element is to be cropped in an outer container, and the clip zone
- Julia's tip 1:  make the zone the whole image:

.clipzone
{
    position: relative;
    width:  500px;
    height: 500px;
    overflow: hidden;
}

.clipped
{
    position: absolute;
}

<div class="clipzone"> <img class="clipped" id="image1" src="" /> </div>

This container is integrated in the flow of the contents of the page with the relative position and allows the content to have the absolution position. The property overflow: hidden avoids exceeding the limit of the container.

so add the clip css property and value into class clipped, and add this rule:
.clipped
{
position: absolute;
clip: rect(200px, 200px, 300px, 300px);   /* top left right bottom*/
}

And then, the image using clip CSS property will be:

Julia's tip 2: 
Add one more rule:
margin-left: -200px;

With the above rule, the clipped image will be positioned at 0 position; in other words, to get any image, for example,
with text: 11, set margin-left: 0px;
with text: 12: set margin-left: -100px;
with text: 13: set margin-left: -200px;
with text: 14, set margin-left: -300px;
with text: 15, set margin-left: -400px;

so the image is always positioned the same place.

References:
1. http://www.w3schools.com/cssref/pr_pos_clip.asp
2. http://www.xul.fr/en/css/clip.php

Actionable Items:

1. clip an image using CSS

https://jsfiddle.net/jianminchen/ksdcgomx/

2. original image vs clipped image

https://jsfiddle.net/jianminchen/hxgakk5n/
1. clipped image: 2. orginal image comparison to the clipped image

Blog reading: 
1. Google keyword search: JavaScript Separate of concern
how to structure JavaScript better?
Study the code - example to follow
 http://stephen-young.me.uk/2013/01/05/maintainable-js-with-modules.html

Watch and learn: Microsoft agile development - Bing






Microsoft Development Services for the DevOps Era

JavaScript - a programmer random thoughts

August 11, 2016

Julia likes to have a small research every day, later she can add some thoughts for the topic. Today the topic is "how to balance coding writing vs reading API documents". 　

In order to write good JavaScript code, read a lot of JavaScript code first. She did write JavaScript/ CSS/ Html code 8 hours nonstop at work, she likes to take a break while she was at home enjoying the evening. 

 Julia reviewed the blog about JavaScript while watching interviews. 

HackerRank: Two string - thinking in JavaScript over 10 ways
  

Interviews she enjoyed - Vogue 73 questions series: 

1. Serena Williams

Serena offers 1 hour $100 master class - video class - She is really good at teaching, she shows in the interview how to make a hidden drop shot.

https://www.youtube.com/watch?v=Gpu_st4ynLc

2. Iggy Azalea - 7 3 questions 

https://www.youtube.com/watch?v=AMh5f8xRLRE

3. Song writer, singer Swift Taylor
https://www.youtube.com/watch?v=XnbCSboujF4

Random thoughts:
1. How to stay calm, answer questions very well?

2. Airbnb JavaScript Style Guide()  - English Version

https://github.com/airbnb/javascript

Reading while going through JavaScript style guide from Airbnb:

1. JavaScript spread syntax...  - 10 minutes

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Spread_operator


3. Read JavaScript Array.From - 20 minutes

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/from
2. Celebrate the day by learning CSS, working on clipping image etc.:

A. clip techniques - outside - relative, inside, absolute
how to define it and practice it!
http://www.xul.fr/en/css/clip.php

B. Text over the image:
https://css-tricks.com/text-blocks-over-image/

C. Bootstrap 3 Thumbnail Slider / Carousel
http://www.bootply.com/XeZvDD059P#

Designing Fluent APIs in C# - pluralsight.com

August 8, 2016

Plan to work on course - Designing Fluent APIs in C#

http://app.pluralsight.com/author/floyd-may

video to watch:
https://www.youtube.com/watch?v=uKtMwmWv6Q0

Mastering C# 4.0 - pluralsight.com

August 8,  2016

Plan to work on this course - Mastering C# 4.0 - pluralsight.com, 11 hours.

http://app.pluralsight.com/author/jon-skeet

C# Design Strategies - pluralsight.com

August 8, 2016

Plan to work on this course on pluralsight.com - C# design strategies - 3 hours.

http://app.pluralsight.com/author/jon-skeet

.NET distributed system architecture - pluralsight.com

August 8, 2016

Plan to work on the course - .NET distributed system architecture - 5 hour 30 minutes

Lecturer's website:

http://app.pluralsight.com/author/scott-seely

Become a Full-stack .NET Developer - Architecture and Testing - pluralsight.com

August 8, 2016

Plan to study the course:

Become a Full-stack .NET Developer - Architecture and Testing

Lecturer's website:

http://app.pluralsight.com/author/mosh-hamedani

Notes:

1. Remaining use cases

2. Modularize JavaScript Code

3. Refactoring towards the clean architecture

4. Programming against interfaces

5. Test Controllers

6. Test Repositories

7. Adding Integration Tests


Modularizing JavaScript Code - 40m 56s

Introduction
Extracting JavaScript Code
Revealing Module Pattern
Refactoring using Revealing Module Patten
Cleaning the init Method
Applying the DRY Principle
Better Separation of Concerns
Module Dependencies
Physical Separation
Optimization
Exercise
Code Review
Summary

Programming Against Interfaces

Introduction
Dependency Inversion Principles
Extracting Interfaces
Dependency Injection
Adding Ninject
Does Entity Framework Really implement the Repository Pattern?
Package Dependencies
Restructure the Application
Complexity Fallacy
Productivity Fallacy
Exercise
Refactoring Data Annotations
Complexity Fallacy
Productivity Fallacy
Exercise
Refactoring Data Annotations
Summary

Testing Controllers


Introduction
Extracting Queries
Repository pattern
When to use the repository pattern
extracting repositories
extracting queries with eager loading
exercise
code review
clean architecture
decoupling from entity framework
unit of work pattern
implementing the unit of work
consolidating dependencies
summary


Programming Against interfaces
introduction
Dependency inversion principle
extracting interfaces


Repository pattern is already in entity framework - no need to use? it depends.

Design to solve problems - repository pattern

complexity of design - be pragmatic

meidum/ large projects

problems :

complex queries/ fat controllers/ fat services


SQL Injection etc. website common attacks -

SQL injection, XSS, CSRF, preventing CSRF attacks -

http://www.veracode.com/security/xss

Blog reading:
August 12, 2016
http://www.peterprovost.org/blog/2012/06/19/adding-ninject-to-web-api

http://stories.visualstudio.com/bing-continuous-delivery/

C# Extension Methods - pluralsight.com

August 8, 2016

Plan to study the course "C# Extension Methods". 3 hours course.

Lecturer's website:
http://app.pluralsight.com/author/elton-stoneman

August 8, 1 hour, Introduction Extension Methods

A small research - tennis coaching vs algorithm lecturing

August 7, 2016

  Julia likes to pick up a small topic to do some research and practice her research muscle. Since she was amazed about USATP master professional Rick Macci's teaching video, and amazed how good the presentation is. A lot of technologies are applied on tennis coaching and tennis matches. For example, on the tennis court, on the grand slam matches, there are hundreds of camera on the court, hundreds of technologies on speed measuring, and all other things.

  Here is the link:

 https://www.youtube.com/watch?v=5MHugAF2DiQ

1. Lecture on Roger Federer's tennis forehand stroke, and show 3D technologies how to do analysis
2. Before vs After, two videos are comparing.
3. Statistics: How many views? over half a million views. -
4. Producer: USPTA
    - how good USPTA can utilize the technologies and help the teaching.

Lecture notes: 
Forehand - 7 steps: (P, J, E, T, F, FS, F)
Preparation
Joint angles
Elbow Extension
Tap the dog
The Flip
Forward Swing
The Finish

Goal: Racket Speed, keep the ball in the court


And teaching lectures she spent time to work on this weekend:

Algorithm: count inversion
extended merge sort:

Julia also likes the lecture content about count inversion - merge sort, the examples and discussions.
So, Julia likes to study those lecture notes, take time to enjoy reading.

1. http://www.cs.umd.edu/class/fall2009/cmsc451/lectures/Lec08-inversions.pdf

2.  https://www.cs.princeton.edu/~wayne/kleinberg-tardos/pdf/05DivideAndConquerI.pdf

3. http://www.cs.colostate.edu/~cs320/Slides/05_inv.pdf

Standford University:
https://www.coursera.org/learn/algorithm-design-analysis/lecture/GFmmJ/o-n-log-n-algorithm-for-counting-inversions-i
https://www.coursera.org/learn/algorithm-design-analysis/lecture/IUiUk/o-n-log-n-algorithm-for-counting-inversions-ii

Julia learns tennis from over 20 top coaches in the world and also actively practice what she learns through lessons:

Here is one of them she learned from the coach - 

https://www.youtube.com/watch?v=n7ApnK3BGcU

Julia started to work on the double alley drill - learning is fun!

one more:

Count inversions - Extended merge sort - 3 Lecture Notes Study

August 5, 2016 

Choose topic: extended merge sort
Algorithm: count inversions

count inversions - extended merge sort
1. http://jane4532.blogspot.ca/2013/06/zz-google-onsite-interview.html
2. http://www.geeksforgeeks.org/counting-inversions/
3. http://www.cs.umd.edu/class/fall2009/cmsc451/lectures/Lec08-inversions.pdf
4. https://www.cp.eng.chula.ac.th/~piak/teaching/algo/algo2008/count-inv.htm

5.  https://www.cs.princeton.edu/~wayne/kleinberg-tardos/pdf/05DivideAndConquerI.pdf
6. http://www.cs.colostate.edu/~cs320/Slides/05_inv.pdf


problem statement:

Inversion Count for an array indicates – how far (or close) the array is from being sorted. If array is already sorted then inversion count is 0. If array is sorted in reverse order that inversion count is the maximum. 
Formally speaking, two elements a[i] and a[j] form an inversion if a[i] > a[j] and i < j

Example:
The sequence 2, 4, 1, 3, 5 has three inversions (2, 1), (4, 1), (4, 3).

Lecture Notes -

1. First lecture study:

http://www.cs.colostate.edu/~cs320/Slides/05_inv.pdf

1. How many inversions at most in the array n?

n(n-1)/2, special case, like {n, n-1, ..., 1}, any two nodes in the array is one inversion pair.

or: What is the maximum number of inversions for a list of length n? 

n(n-1)/2

2. If each inversion is counted once, then the time of the algorithm is O(n^2), n is the number of elements in the array. Not optimal, we should not count each inversion.

3. Ideas to solve the algorithm:

Bubble sort? 

Selection sort?

Insertion sort? 

These are O(n^2)

Bubble and insertion sort count each individual inversion. To do better we must not count each individual inversion. 

So, better algorithm is to beat O(n^2), using merge sort, nlogn - divide and conquer - sort and count inversion in the same time.

In merge sort we do not swap all elements that are out of order with each other, we make larger distance "swaps". 

Questions: Sorting and counting inversion - merge part how to count the inversions.

Keywords in the lecture notes (7):

Collaborative filtering 

inversions 

Meta-search tools
Rank analysis
Recurrence Analysis  - T(n) = 2 T(n/2) + cn 

similarity/ dissimilarity / in the middle 

the number of out of place rankings 

Actionable Items: 

1. Merging part with diagram:   <- Julia, can you draw a diagram as well 

2. Count Inversions: Algorithm pseudo code - write down here: 

2. 2nd Lecture Notes Study: 

https://www.cs.princeton.edu/~wayne/kleinberg-tardos/pdf/05DivideAndConquerI.pdf

Julia, write down favorite notes one sentence a time, on page 16, 17 

------- 

Counting inversions: how to combine two subproblems?
Q. How to count inversions (a,b) with a ∈ A and b ∈ B? 
A. Easy if A and B are sorted!

Warmup algorithm. 

Sort A and B. 

For each element b ∈ B, 

- binary search in A to find how elements in A are greater than b. 

list A                               list B

7    10    18  3  14           17    23    2  11  16

sort A                              sort B
3   7    10  14  18            2   11    16  17  23

binary search to count inversions (a, b) with a ∈ A and b ∈ B

3   7    10  14  18            2   11    16  17  23
                                       5    2      1     1   0
-------

3. 3rd Lecture Notes Study:  (Inversions Count)

http://www.cs.umd.edu/class/fall2009/cmsc451/lectures/Lec08-inversions.pdf

Play to win; stop Recognize when you are using negative self-talks and replace it with positive; when in doubt, remember: Play to win.

Great tips for sports coaching, https://t.co/6m29a8l1z0

— jianmin chen (@jianminchen) July 22, 2016

Memorize 8 tips to help you to perform to your highest potential in Tennis (? code practice, etc.):
1. Let go of what others think
2. Perform for yourself, not to impress or to "not disappoint" others
3. Accept that you will make mistakes, and let them go
4. Focus on what you can control
5. Recognize when you are using negative self-talk and replace it with positive
6. Rather than performing perfectly, perform to see improvement
7. Be objective about your performance, not subjective
8. Focus on the Journey, not the Destination

Play not to lose or Play to win - Julia plays to win! 

Some people play not to lose. I play to win each and every second I'm on court. #SpeedTakes aggression. pic.twitter.com/ae5xlriogs

— Simona Halep (@Simona_Halep) July 2, 2016

ITINT5: tree maximum path sum (II)

August 4, 2016

Blog 1: July 6, 2015
http://juliachencoding.blogspot.ca/2015/07/itint5-tree-maximum-path-sum.html

First writing in C# (July 6, 2015)
https://gist.github.com/jianminchen/754d29e47c491cfc271f764fb5dd8a61

Review comments (August 4, 2016, after 13 months):
1. first, the input argument res - variable name - not accurate - res should be maxValueCrossRoot
2. function name: maxTreePathSumRe is confusing, will be better called "maxTreePathSumEndByRoot"
3. line 121, 122 can be merged into one line statement - easy to read 
4. add some design spec for the function - maxTreePathSumRe

Blog 2: August 4, 2016
C# code practice: 2nd writing
https://gist.github.com/jianminchen/c9be400e7bee71734ee7c454635846cf

review comments:
1. Line 138 - 150, function ArrayMaximum
No need, call Array.Max();

3rd writing:
https://gist.github.com/jianminchen/3b2c8e0e84e52cbca2a7ec435b29a2e4

highlight of changes:
1. line 124, use Array.Max(), remove the function: ArrayMaximum(int[])

Use Language Integrated Query (LINQ) - Array.Max(), detail see the blog:
http://juliachencoding.blogspot.ca/2016/06/array-class-c-c-javascript-java.html

LINQ - Enumerable Methods Reference:
https://msdn.microsoft.com/en-us/library/bb342261(v=vs.100).aspx

Blogs to read:
Choose topic: extended merge sort
Algorithm: count inversions

count inversions - extended merge sort
1. http://jane4532.blogspot.ca/2013/06/zz-google-onsite-interview.html
2. http://www.geeksforgeeks.org/counting-inversions/
3. http://www.cs.umd.edu/class/fall2009/cmsc451/lectures/Lec08-inversions.pdf
4. https://www.cp.eng.chula.ac.th/~piak/teaching/algo/algo2008/count-inv.htm

Practice makes possible. https://t.co/Y9JyWKwLKY

— jianmin chen (@jianminchen) June 11, 2016