Saturday, November 18, 2017

Week of code 35

Nov. 18, 2017

Plan to play week of code 35 starting this Saturday. I am getting excited on the contest.

Comparable Interface lecture notes

Nov. 18, 2017


I have chance to go over the lecture notes called Comparable Interface, and I like to share my review of lecture notes, how good it is for me to learn things after over 10 hours practice on Comparable Interface. The lecture note is here.

Code review: Dynamically sorting with IComparer

Nov. 18, 2017


One of challenges is to ask a good question on code review. As an experienced code reviewer, I certainly understand that Order Strings should be a good candidate for my next question I try to find last few days. Even though I spent over 10 hours to practice Order strings algorithm and got a lot of training, but I still knew that I need to be mentored. One thing is to look into previous code review on IComparer.

Code review study

Dynamically sorting with IComparer

What is Int32 in C#?

Nov. 18, 2017


Learning by myself is such a great journey, I had a best world interview in the world this October to be tested how good I understand the object-oriented programming. I know that I am kind of weak, I have no clue to figure out my weakness from senior level programmer in well-founded biggest company. I try to dodge questions but I know one day I have to catch up.

I need to read Int32 C# source code. How do I find time to read the code and get the idea? I was so busy with my full time work and learning by myself. So many things to do, how do I have a clue to study this and break through the foundation of learning object-oriented programming.

Order Strings

I played the contest and wrote a partial sorting algorithm called Order Strings. Followed up hours of study code submission, over 10 C# submission with full score, I reviewed the code and wrote Order String Series blogs about the practice. But I still felt that I need some more coaching. 

Code review study

I found the best code review about IComparer. Because this statement is telling the fact, but I never know that.

Sort algorithm on Leetcode

Nov. 18, 2017


Sorting is most basic algorithm in computer science. Here is the list of sorting algorithm on Leetcode and I like to review them.

On Nov. 15, 2017 10:00 pm, I practiced sort algorithm and my peer is a Chinese with over 10 years programming experience in USA. The peer gave me the excellent code review and made some great comments.

Let us first take a look at the overall evaluation. C# code is here.

So and So

It is my evaluation of coding on a sort algorithm. Things you should work on: No clear thought, messy coding. Here are the code review I got:

Transition from bottom up to top down

I went through bottom up approach to write a functionality of findMaxIndex by the help of whiteboard test with a simple test case: [1, 5, 4, 3, 2], I explained to the peer that I like to find index of max value of the array 5 first, and then second step is to move 5's position to the first element in the array, and then move first position to the last position of the array using flip API twice.

The peer complained that what is line 38 and line 39, it can be written as swap(arr, maxIndex + 1, subArrayLength). If you have time, then you can write the function, ask the peer if you should write the function or not, basically two flip calls. 

Same story applies to line 24 to line 36.

The small research I have to do is to figure out if top-down approach is really great and I should learn. When I do not have clear solution for the algorithm, I often choose the bottom-up approach, use a simple test case to do whiteboard testing, write a working solution first. And then add on the solution. But I should not stop, need to add review, use top-down approach to extract functions, make meaningful names.

CountFound variable is not meaningful, it is better to use subarrayLength.

I can not hide what I do at work, if I code messy at work then I will show up messy in mock interview.

Friday, November 17, 2017

Linkedin 950 connections study

Nov. 17, 2017


One of my most favorite activities is to review my connections on linkedin at the end of 2017. Over one hour, I went over connections by shared connections and tried to collect some statistics, and see how my friends make their career movement, how they advance their career.

I started to see how many of them moves to Amazon, and then went over others and found out what kind of jobs they change.

Now it is 11:48 PM, I started from 10:00 PM. I started to 10:00 PM since I believed that I booked the mock interview, and then I toured LinkedIn and just got lost in those connections.

What to study 

I have over 900 connections, first I went over my messages history last 12 months and found out over 90 mock interviewers's update. So surprisingly, a few of them got jobs in Facebook (2), Amazon (4+), and Microsoft (2+). I checked their job history and understood how they are selected. Some of them have solid work experience through last job, over 4 years, well-established companies.

The list of companies I looked up are Microsoft, Google, Apple, LinkedIn, Amazon, HP, ITW, Oracle, Sony, Intel, Motorola, Florida Atlantic University, etc. I added some friends through mock interview, and started to learn how new generation of people work compared to my old friends, from Intel, Intuit, Cisco, Qualcom, etc.

Wednesday, November 15, 2017

Binary tree root to leaf path minimum path value with the path

Nov. 15, 2017

I like to document my mock interview practice on this algorithm. The topic is about analysis of the algorithm, how to reason to find possible bugs?

Here is C# practice code.  I added line 27 to line 32 to fix the bug since the peer told me that the edge case with no children. The advice from the peer is "After writing the code need to analyze more before running it". 

Story of analysis

I need to explain how the depth first search works since peer asked if I should add an argument of function to pass the existing value. I did explain the algorithm in the mock interview, but the peer felt that he did not know C# very well and got confused. 

I like to write my story to show how I analyze the algorithm after the mock interview, try to make the explanation to a very good one. 

Let us go over  a tree with the following nodes:

  /   |   \
 4   3   6

The depth first search algorithm can be solved this way. The root node with value 0 has a tree, to find its minimum path to the leaf node, first if the root node is null, then value is 0; if the root node is not null, and if the root node has no children, it is a base case, the minimum path is the value of root. Otherwise, go over each children of root node with value 0, and go to each child in the array [node 4, node 3, node 6], and ask each node to get its minimum value for the path, denoted as Mi, and just add root node value 0 to Math.Min(Mi, i from 0 to 2).

Miss a base case

From the above paragraph, I highlighted the base case I missed in mock interview using brown color, and the peer had to tell me that there will be a problem if there is no children. In other words, in the tree showing in the above diagram, if the root node with value 0 has no children, it is a base case, the minimum path is the value of root.

Order string (VII)

Nov. 15, 2017

I like to write a blog about this C# practice, using Linq IList.Sort method. The link is here.

Order string (VI)

Nov. 15, 2017

Algorithm Study and Code Review

Here is the code related to the algorithm. I like to write a blog on the code. The main idea is to use primitive type string, just add index to the first element of string array, avoid a struct or a class definition. Kind of tricky. 

Follow up study 

Nov. 16, 2017

It is always a good idea to search code review to read IComparable<T> code review. I sepnt over 20 minutes to read the algorithm: Dynamically sorting with IComparer. And one of statement in the code review reads like the following:

public int CompareTo(ProductSortAttribute other)
    if (this.Index == other.Index)
         return 0;

    if (this.Index > other.Index)
         return 1;

    return -1;
can be shortened to
public int CompareTo(ProductSortAttribute other) {
    return this.Index.CompareTo(other.Index);
Since Int32 also implements Comparable<T>.

What is Int32?

Here are a list of things Julia starts to her independent study:
1. What is Int32? A structure
2. What interfaces does Int32 implements? IComparable<T>, IFormattable, IConvertible.
3. Where is the source code of Int32 in mscorlib? Link is here.

Comparable <T>  study

Sometimes, it is so easy to find an excellent lecture notes, and then I can follow quickly how to write basic comparer. Here is the one.

Order strings (V)

Nov. 4, 2017


It is fun to continue to work on C# practice on this algorithm called order strings.

I reviewed the code and made some change, C# code is here for me to review later.

Tuesday, November 14, 2017

Order string (IV)

Nov. 14, 2017


It is my favorite C# code to study, through the code, I can tell that the player has more C# coding experience compared to me, and also the trick used to do numeric comparison to make code so simple and only take one line of code, referring to line 44.

I just could not believe that the experience the player has and it makes coding so enjoyable experience, like a competing sports.

I could not express more enjoyment to read other people's code. When I read those excellent engineering idea, creative idea to solve the problem, I cannot believe that it makes coding such a challenging sports and I am just glad to be a follower.

Code study

I reviewed the code and rewrite the code, here is the code. I have to push myself to get LINQ to my daily coding practice, so I am ready one day to write a web application with much better code using LINQ.

Relax your mind 

I like to use this video to relate to read an excellent engineering idea to deal with solving problem.

Order string (III)

Nov. 14, 2017


It is the best time to learn C# programming using one of medium algorithm in the Morgan Stanley codesprint. The design of algorithm includes using BigInteger class and also LINQ OrderBy and OrderByDescending.

Code study

I reviewed the code first, and then I rewrite the code. C# code is here.

Order strings (II)

Nov. 14, 2017


It is time for me to learn how to write a C# program and also review other's code. The second study code is written using SortedDictionary. DescendingComparer class and DescendingComparerI class are defined.

Code design talk 

Here is the C# code after I review the code.

Order strings (I)

Nov. 14, 2017


It is the time for me to study code submission using C#. This is the first C# code submission I studied, delegate is the keyword used in code, and also string.TrimStart.

Here is the C# code after I reviewed the code.

Code design talk 

The structure is used and called OrderString.

structure  OrderString
    public int      Index;
    public string Lexicographic;

Monday, November 13, 2017 - becoming an outlier

Nov. 13, 2017


It is such a great privilege that I got subscription of monthly. It is time for me to review how many hours I spend on last 12 months.

I like to revisit the course called becoming an outlier: reprogramming the developer mind by cory house.

Course study

Plan to take some notes and do some research from lecture notes.

Do it yourself - Auto maintenance work

Nov. 13, 2017


Once a while, I find myself in the trouble to keep up with knowledge of automobile, so I have to learn a few things through For example, how to install a car battery? I did once recently. This past October, how to put a backup tire, that was my favorite research through, I got a flat tire and then I like to do some research how to fix the issue by myself.

My research is so shallow this October, I watched 2 or 3 videos to put a backup tire, and then I tried to do it myself, I could not take off lock nut off no matter how hard I tried. So I went back to watch videos, until a few hours later, one of videos shows that it is to use your feet to leverage the power. I used the tip and solved the problem puzzled me more than 2 hours.

Learning is fun

I sent my car to Canadian tire auto repair last Monday for 4 pm appointment, and I was told that the tire cannot be repaired, so two new tires will cost more than $300 dollars. I politely declined the advice, and waited last Saturday and then drove to O Tire, and I got the tire repaired. There are two nails in the tire, the cost of repair is $60 dollars, with life time warranty.

I spent 10 minutes to touch all tires's tooth in O Tire store and try to understand the technology of tire.

My low beam light

One of my weakness is to be patient and be able to solve real problem in my daily life, walk away with things like wechat talks, reading or sharing. I need to take care of a lot of things, like maintaining good friendship with Christian friends, sometimes it means a long lunch together with group of people.

I checked tonight that two of low beam light bulbs stop working. I found that low beam light has some issue, but until today in the dark outside of the home, I did make sure that light bulbs do not work.

To be outlier

It is time to review the course I learn from called "Become an Outlier: Reprogramming the Developer Mind", I did in July 28, 2017. I plan to revisit the course again and try to apply the learning to my daily life.

Sunday, November 12, 2017

count pairs

Nov. 12, 2017

Plan to study the hard level algorithm called count pairs, the problem statement is here.

Moving Elevator

Nov. 12, 2017

Plan to study 30 minutes a time on this hard level algorithm called Moving Elevator. The problem statement is here.

Check the leaderboard and also find a googler with code submission, the linkin profile is here.

How to convert finite automata to regular expressions?

Nov. 12, 2017

Plan to study the stackoverflow question How to convert finite automata to regular expressions?

Stock porfolio - Morgan Stanley campus codeathon 2017

Nov. 12, 2017


It is such a great contest for me to play last weekend. I was pushing myself to get back to play coding contest and then train myself to work on hard level algorithm. The first two medium level algorithms in the contest are so helpful for me to catch up learning on C# programming and also warm up the statistics. As a software programmer, I learn that the contest does not require me to write very complicate code, I need to stay cool and also think about the foundation of statistics sometimes, need to refresh my knowledge and quickly look up.

Algorithm study 

Plan to work on the hard level algorithm called stock portfolio, Morgan Stanley campus codeathon 2017.

The problem statement is here.

It is also a hard level algorithm, my favorite algorithm to learn and apply some dynamic programming techniques.

Miss my mother and she will be remembered

Nov. 12, 2017


It is the the first Sunday I will live without a mom in the world. She passed away on Nov. 11, 2017 at the age of 86.

My mom was such a great person who had lived her life to the full. I have so much good memory to spend time with her. Specially after I went to college, she still corrected me when I made mistakes, and she answered my phone calls when I felt lonely a lot of years, and we lived together back in Florida together back 4 months in 2000 and 5 months in 2001.

I will go to Willingdon church this morning, and I like to pray and wish everything is great with all I have.

God blesses us, have a wonderful Sunday.

Nov. 25, 2000
Julia with her mom qingfu liu in Orlando, Florida, Seaworld theme park.

January 26, 2012

2014 Chinese spring festival

Julia interviewed her mom how to celebrate China new year. Here is the link on

Julia took care of mom while she played tennis and had some conversation with her mom. Here is the link on

Julia walked on beach with her mom in 2012. The video link is here on facebook.

Oct. 13, 2017, 3 PM, first time in my life, I washed my mom's feet with the help of 3 other sisters.

Bible teaching is very good about washing each other's feet. I shared my learning with my sisters, and they all liked the idea and helped me to wash my mom's feet first time.

Quora study: Shriram Krishnamurthi

Nov. 12, 2017

Plan to study a computer professor and how he thinks in terms of education, computer science, quora platform, and other things.

The quora profile is here.

Saturday, November 11, 2017

Order strings

Nov. 11, 2017


It is the first medium algorithm in Morgan Stanley Campus Codeathon 2017. I spent a few hours to work on the code. Now it is 11:54 PM. I am trying to get more points. What should I do to get more points?

The problem statement is here.

I am very patient to read problem statement again and again, try to find the clue what is missing in my problem solving. Look at those test cases:

Follow up after the contest

Nov. 12, 2017 9:43 pm
Julia tried a few submissions. Here are the link to her C# submissions.

First submission, only score 8 out of 40. Here is the C# code of first submission.
Second submission, only score 5 out of 40. Here is the C# code of second submission. Change numeric type from int to long, score from 8 lower to 5.33
Third submission, numeric type, consider the length of string 50, check one char a time. Score goes up from 8 to 23 out of 40. 
Fourth submission, C# code is here

Plan to study all C# submissions.

The great game of Galia

Nov. 11, 2017


It is the first medium algorithm of Morgan Stanley Campus Codeathon 2017. Now it is 7:38 PM, Saturday evening. I like to spend some time to work on the first medium algorithm.

I like to make this algorithm as simple as possible. Let the fun begin.

Now it is Nov. 12, 2017. It is 12:22 Am. I fully understand the problem statement, and also I like to code something for my contest.

Since the contest will end in Sunday morning 10:00 am, I am better to go to sleep and get up early at 6:00 AM to work on the contest. Now it is 12:47 AM, better to sleep on this algorithm.

Next step 

I woke up 6:30 AM, but I enjoyed the long stay on the bed with music and wechat reading. Now it is 9:32 AM. The contest will end in an hour. I need to work on something.

Read quickly on the algorithm leaf node count on binary search tree. The link is here.

These are steps:
1. Find all sequences
2. Construct binary search tree
3. Count leaf node
4. Add to the sum
5. Evaluate the algorithm time complexity and space complexity
6. Try to optimize

There is timeout issue. So I have to use dynamic programming, using combinatorics, and build a recurrence formula. So the code should be very easy.

Now it is 9:56 AM, the contest is extended to 10:30 AM.

I like to show my worksheet, and it is my way to push myself to work hard on algorithm, no matter how hard it is.

Friday, November 10, 2017

Eight years is like a blink of eye

Nov. 10, 2017


It is like the blink of eye that I have spent almost 8 years in the city of Vancouver starting from April 18, 2010. I still remembered the conversation, plans my friend prepared for the 14 days road trip from April 1 from Florida to Vancouver, in the year of 2010.

I like to celebrate my hard working eight years!

Plan to write an answer on how I planned the trip with a friend over 14 days.

Thursday, November 9, 2017

What is the third algorithm to ask code review?

Nov. 9, 2017


It was 11:10 pm, and I spent over 30 minutes to go over the algorithm I practiced, and try to find a good one to ask code review.

Now it is 11:45 pm. The one I am reading now is leetcode 212 using trie data structure, the blog is here.

I came back from a break this September and asked two algorithms based on my mock interview practice. Today I like to find the third algorithm to ask code review.

Algorithm review


It is also good warm up to review my favorite practice and share with the community.

Plan to study the algorithms of Trie from code review website, Trie implementation for left to right wildcard search, and another one: Trie (tree form) in Java

4 Sum

It is Harvest Time! (1 Corinthians 3: 5 - 9) (I)

Nov. 9, 2017


It is time to review what I have completed on mock interview, I have completed almost 4 rounds of mock interview. I like to review what I learn, and show some analysis what I did good or wrong.

Let me first to give a topic for my blog, I google using keyword it is harvest time. Here is the preach I like to go over and see if I can write similar blog to document my learning. Here is the preach link, It is Harvest Time! (1 Corinthians 3: 5 - 9).

It is Harvest Time!

There are four stages to get to the harvest, prepare the soil first, sow the seed, cultivate the soil and reap the harvest.

I spend 10 - 20 minutes to go over those 28 interviews, and I read the comments for each interview. And I just enjoy the work I have completed. No matter I stumble on the algorithm or fail to help the peer, I go through the learning process.

My best teacher to help me write this series is this Moody bible institute professor, who writes very well on this article. Pastor Keith Krell is here.


This is the first time I finished over 28 mock interviews, and I remembered the worst performance to solve a Sudoku algorithm, I got rate 1 out of 7 for coding on April 11. After six month, I posted the question on code review on the algorithm on Nov. 6, 2017, here is the link called "Sudoku solver with clear structure". 


1. First round mock interviews, 27 interviews.


C# Array class document reading

Nov. 9, 2017


It is best investment of time to read C# Array class documentation. What I do is to print out a copy and hold the copy to read again and again, ask questions, take notes, and write down what I learn.

Here is C# Array class, I do not have chance to go over the object-oriented design course, but I like to ask myself to memorize all APIs, and also be able to clear all the terms shown in the document.

As a programmer, I like to write code quickly using existing API of Array class, and be able to understand those interfaces as well. I find out that I am interested in the discussion on stackoverflow on those C# interface, and I try to figure out what the difference is.

Read like bible 

I like to read C# Array class like bible. I will mark those words showing in the document, and then I will use those words when I need to write blogs about the algorithm.

C# Array abstract class source code scout

Nov. 9, 2017


It is the first time I read C# class Array's source code through Microsoft website. I spent a few hours t o read over 3000 lines of code. I call it scout since I have written a few blogs about C# Array but it is the first time I have chance to read C# code.

Take notes, please!

It is so interesting for me to read C# Array class, so I have to be able to understand why it implements five interfaces and it is an abstract class. I am very curious about how the code is structured in one class over 3000 lines of code.

Read C# Array source code here. I found the link in the first few paragraphs of Array document.

Read C# SorterObjectArray - mscor.lib, the link is here.

Plan to write down some notes to help myself to continue to get educated on C# Array, and understand the design of .NET framework. 

Leetcode 151: reverse words in a string

Nov. 9, 2017


It is in-place to make the algorithm a classical algorithm for any language. I have practiced over a few times last 6 month, and on Nov. 8 10 PM I had chance to write the algorithm in 30 minutes, and the code passed all test cases.

Usually first few time I have to figure out the issues I have and then found ways to solve the algorithm. Last night practice is no longer challenge for me anymore, I noticed that and started to look into Leetcode 151 discussion panel after mock interview.

Algorithm study

Here is the C# practice.

Quora read: Thanh Trung Nguyen

Nov. 9, 2017

Plan to read Thanh Trung Nguyen, the profile is here.

Wednesday, November 8, 2017

Quora read: Lalit Kundu

Nov. 8, 2017

Plan to read the answers from Lalit Kundu, here is the quora's profile.

My favorite question is about implementation skills. The answer is here.

Leetcode 10: regular expression - Fun to play

Nov. 8, 2017


It is really fun to play with code related to recursion tree after the mock interview. I ran into various error with a simple test case each time using Leetcode online judge, I learn from each failure and try to play with them. It is fun to play over hours and actually I like to learn something here. Let me document the issues first, and then figure out the solution later.

Test cases to help 

I like to list the test cases to help design the algorithm.

"", "a*"
"", "a*b*"

Here is the C# code with a bug timeout - need to run at least 1 time first for a* pattern, and then run 0 time for a * pattern.

The test case for time out is here:

And the code causes the problem is shown in the following picture:

Here is the C# code with fix of timeout:

Catalan number

Nov. 8, 2017

I will write something here about the algorithm. Will come back very soon.

Transcript is here. I will write down the story later on.

Tuesday, November 7, 2017

Leetcode 10: regular expression

Nov. 7, 2017


It is such an adventure to work on Leetcode 10: regular expression. I chose the algorithm as my most favorite mock interview algorithm on last month, the link is here. But of course I was so nervous since I could not believe what I will write down.

My practice 

The peer was very nice and also helpful. I went over each test case and explained the matching, and I told the peer that I will use one of test cases to do whiteboard testing, recursive tree I will use at least 2 branch. For any char followed with *, I will match 0 time or 1 time or more than 1 time.

Here is my C# practice code. I ran the test cases, the code failed the test case with "" and pattern "a*". So I tried to fix it, added one base case, but still failed the test case. The code is here.

I told the peer that I will fix it after mock interview. I already took 43 minutes. Such a great workout.

Discussion between two peers 

Here is the discussion between two peers in mock interview:

how do you match "abb" with pattern "b*b"? Peer asked, and he put down the test case next to line 68.

I think that there are 3 branches in recursion tree:

b* match 0 time, so "abb" will check to match "b", return false;
b* match 1 time, so  'a' != 'b', return false;
more than 1 time will also return fail.

Let us check "bbb" with pattern "b*b", Julia suggested to work on.

We like to check 0 time, 1 time or more than 1 time.

For 0 time case, "bbb" will try to match "b" since "b*" 0 time means empty string. Return false;
For 1 time case, b matches b*, so "bb" will try to match "b", return false;
For more than 1 time case, "bb" will match "b*b", go back to 3 cases, return true.

Show some image to help understand the discussion:

Feedback from the peer

I just could not believe that the peer was a competitive programmer in high school, and then he just finished his computer science graduate school two months ago. He showed to me how strong his analysis was to handle the algorithm and coding was fast and quick later on, he finished in 12 minutes and it seemed to me that he got very good training on the algorithm. Will continue on my next blog Catalan number on the performance. The peer played contest on

Follow up 

Nov. 8, 2017
The code is updated with code from line 37 to line 41 to fix the base case, empty string "" matchs "a*" pattern string.

C# code is here.

Two peers comparison

It is interesting to know that two peers can evaluate each other with top rating, but how about to compare the profile of two peers and see what we can tell from those numbers.

Divide to n small linked list with length difference at most one

Nov. 7, 2017


It is the first time I went through a friend met in mock interview, we both worked on the same algorithm together. I wrote two version of code, one is recursive function, one is iterative one.

Problem statement can be written in the following:

Given a Linked list, split it into x number of smaller linked list where the size difference between any two list should be at most 1

Algorithm practice

It is so interesting to have discussion with the peer outside mock interview platform. I always think like a math major graduate student, the first 5 minutes I will go over anything including mathematics, and then I rested all time. Since I went through the linked list practice in 2016, here is one of linked list practice blog to document my practice. 

I like to observe how the peer picked up the analysis and worked hard on the coding. For me, it is just another routine and I do not need to think about too much. 

C# code is written here, and later on I will compile and add some test cases. 

First, I wrote a recursive solution. The link is here. And then I wrote an iterative solution, the link is here

Also, I like to give the code review for the peer's code. The code is here


Time spent in discussion 7:15 pm - 9:18 pm