Being an interviewer: Find the duplicate number

April 4, 2018

Introduction

The algorithm is my favorite one. I learned a few days ago by a peer, he tested my algorithm problem solving. Here is the quora's link related to the algorithm.

In order to learn better on the algorithm, I gave it to the peer who is preparing Google onsite. I like to figure out how he will solve the problem.

Problem solving

Here is the script for the mock interview. I will write down a few lines of notes for the mock interview later.

Being an interviewer: Leetcode 84: Largest rectangle in histogram

April 10, 2018

Introduction

It is my favorite algorithm and it is hard level algorithm in Leetcode.com. I chose this algorithm to interview a friend met on mock interview. He is preparing next week Google onsite, and I gave him another hour mock interview.

I practiced the algorithm recently, but I found out that I still missed something important. The optimal time complexity is O(n), and it has to use stack to save the index of rectangle left boundary when ascending. The stack is always keeps non-descending heights. Here is the link for my past practices.

Learning is fun

The peer is very organized and also very good at explaining the algorithm. I specially like the way he structured the content.

Here is the script for the mock interview.

Missing Florida summer 2009

April 8, 2018

Introduction

I spent 14 years to live in Florida from 1996 to 2010. I miss the fun to live in the city of Boca Raton and like to document some fun memory. I also like to clean up all photos and videos I took for those years. I like to get some idea how to make good memory for my life events.

Florida Atlantic University campus

2010 Buntzen lake hiking trip

April 7, 2018

Introduction

It is such a fascinating world. I had such great time in Florida from 1996 to 2010, I always stayed near Florida Atlantic University campus, so I worked on my computer science PH.D. study from 2001 to 2010, so I hanged out with Ph.D. students and scholars all the time. I landed to Canada in April 18, 2010. At that time, I did not have a job waiting for me, I just landed as a permanent resident.

In May 24, 2018, after one month I landed in Vancouver, looking for a software programmer job in the city of Vancouver. I was invited to go out hiking with my Shanghai Jiaotong university's classmate Zhuang and her family.

First time challenge

I used to stay in Florida all the time. So it is so surprising that I had difficult time to do hiking trip with a group of 20 people. So amazing, I experienced the joy and nature beauty of Canada and people I started to get to know.

At that time, I only had two Shanghai Jiaotong university graduates I knew working in the city of Vancouver.

Instagram photos

I like to post some photos for the hiking trip. And also one video.

I like to take some break and think about how important it is to enjoy a Saturday, hold on my plan to work on mock interview, algorithm problem solving, pluralsight.com course responsive website etc.

One video - I like my voice

I talked to my roommate Emma and she said that my voice is not aging at all. I like my voice. Here is the video I recorded at the top of mountain with my friend Zhuang and all other families. I missed the fun.

Count down China vacation

April 7, 2018

Introduction

I will have a very short vacation to China this April 12 to April 18. This is the first time I made the choice to vacation in April.

First of all, we have get-together after 30 years, we graduated with applied mathematics from Shanghai Jiaotong university. We chose one week just after Shanghai Jiaotong University 122 years birthday April 6 celebration.

I spent a lot of time to read wechat group 500 people of Shanghai Jiaotong university just setup for Shanghai Jiaotong university 1988 graduated students. Suddenly, I had to challenge my memory to recall all those faces. I have no clue who they are. But once the pictures together with 30 years before/ after, my memory is coming back.

Life is such a beautiful thing with so many talent friends graduated in 1988 sharing the memory together using wechat.

Not all of us are huge success and very good career. We do have some of us to complain that they work for the big manufacture business, and went through the hard time to lose the stable job, and then the transition to the challenging life.

But we do have a lot of successful stories, in my class 70141, there are principal scientist, professors, deans of universities, math teacher and bankers one of 3600 banks in China top executive etc. We are lucky since we chose to study mathematics,  we had less than 30 people in the mathematics major in Shanghai Jiaotong university admitted in 1984. But at that time, we have more than 6 class of mechanical engineering major, material science major etc.

Leetcode 312: Burst balloons

April 6, 2018

Introduction

It is a hard level algorithm, so I like to work on the algorithm over ten times. I like to spend time to read this blog written in Chinese, and then try to understand better about the algorithm.

Here is the gist I created for blog study.

My favorite algorithm

It is the first time I read this analysis in Chinese. I could not believe that the analysis is such a good one.

I have to learn how to break into two subproblems and also two of them are independent.

Algorithm study: 95 algorithm videos (VV)

Algorithm study: 95 algorithm videos (VIIII)

Algorithm study: 95 algorithm videos (VIII)

Algorithm study: 95 algorithm videos (VII)

Algorithm study: 95 algorithm videos (VI)

Algorithm study: 95 algorithm videos (V)

Algorithm study: 95 algorithm videos (IV)

Algorithm study: 95 algorithm videos (III) - Leetcode 5: Longest palindromic

May 4, 2018

Introduction

It is six minutes teaching video for Leetcode longest palindromic substring. Here is the link.

Algorithm study: 95 algorithm videos (II)

April 20, 2018

Introduction

It is hard level algorithm called Leetcode 312: Burst Balloons. And the video is 20 minutes, I spent the time to watch the video, staying at home for one day vacation. I enjoyed the learning of the algorithm.

It is interesting for me to learn the dynamic programming through the video. I like to evaluate the author and see how good he is. I know that he is working for Facebook.

Leetcode 312: Burst Balloons

I like to talk about a screenshot and discuss the layout of dynamic programming algorithm presented by basksetwangcoding.

First step, I need to define state for the dynamic programming algorithm.

Next step, I need to define initialization step.

Third step, I need to define the function, problem and subproblem how to connect each other.

[left][right] = Max(i: [left + 1, right - 1])

For each subproblem, coin[i] * coin[left] * coin[right] + [left][i] + [i][right - 1]

Fourth step, I need to define result: [0][n - 1]

I need to put together a simple example to explain the solution to the peer. Here it is the example:

  1    2    3    4   5   6   7  8  9

Algorithm practice

Here is my C# practice.

Algorithm study: 95 algorithm videos (I)

April 6, 2018

Introduction

It is a hard level algorithm called Leetcode 312: Burst Balloons in Leetcode.com. I like to study the algorithm again by watching the teaching video here.

I could not believe that I finally have time to write code for the algorithm on April 25, 2018.

Leetcode 312: Burst Balloons Algorithm practice

I started to work on the algorithm on April 24, 2018. I have to learn the algorithm by working on a simple test case [3, 1, 5, 8] with the maximum value 167 based on Leetcode 312 problem statement. What I did is to write C# code based on the idea based on the video provided by a facebook engineer.

I calmed down and thought about how to write this dynamic programming solution, I told myself that I should take the time to think and do not rush, read other people's source code.

Basic ideas are simple. Define the base cases first, and then bottom up build the dynamic programming table.

I spent more than 40 minutes to write down the code on the paper. I put the code in Visual studio and debug the code. Apply the test case [3, 1, 5, 8]. But the code does not work, the value is much bigger than 167. Actually it is 218.

Here is my C# practice with some bugs. I need to figure out my problem in the algorithm. 

I could not believe that I could not count the correct number. The number is too big. In theory, it should be the error from the base case, the logic of recurrence is simple and I copied from the facebook engineer presented in the above video. But I need to train myself on this bug finding process. 

Find the bug

It is time for me to read discussion panel of Leetcode 312, I read a few of them, but the dynamic programming idea is different. So I continued to google and read a few blogs. One of blogs is very good since the blogger works for Microsoft.

But I still could not apply my case. The dynamic programming method in those blogs are inclusive, not exclusive.

Questioning the base case

Finally I started to question my base case, what is the value dp[i, i+1], in other words, keep ith and (i + 1)th balloon, then there is no balloon to burst. My answer is numbers[i] * numbers[i + 1], that is too much. So I changed to one. I ran the code still not the correct. So I finally know that it should be 0.

Although it takes me a lot of hours to learn the algorithm, but I think that I do right thing for myself.

Here is my C# code to pass Leetcode 312 online judge.

Algorithm study: 95 algorithm videos

April 5, 2018

Introduction

It is very surprising that those videos are very well prepared by a facebook engineer in Chinese language. I really like to learn something from the teaching.

Here is the video feed. Here is the author's profile on leetcode.com.

10 most favorite algorithms

I like to choose my 10 most favorite algorithms and write down some notes here. I like to study some algorithms so that I can prepare some good questions to be a mock interviewer for a peer who prepares for Google phone interview second round.

I just could not believe that I had last 2 mock interviews as interviewer, and two peers are preparing for Google onsite in a week. I can tell how good they are to prepare for the interview.

Leetcode 84: Largest rectangle in histogram

April 5, 2018

Introduction

It is time for me to learn this hard level algorithm again. I know that it takes at least 10 practice for me to learn a hard level algorithm. Today I chose to study the video prepared by basketwangcoding in Chinese. My last practice was on January 18, 2018. Here is the blog.

30 minutes video lesson

I like to write down some notes from the lecture.

Brute force solution


In order to learn the algorithm very well this time, I like to work on the test case, [2, 4, 6, 5, 3], explain to myself how to solve the algorithm using O(n^2) brute force solution first.

How many rectangles to be calculated? What is the maximum rectangle area's value?


Iterate the end position from i = 0 to 4.

i = 0, the rectangle is 2.
i = 1, the rectangle is 4.
i = 2, the rectangle is 6.
i = 3, the rectangle is 5 + 5 = 10
i = 4, the rectangle is 3 + 3 + 3 + 3 = 12.

So the maximum rectangle is 12.

For each end index, we can go backward to search until the array's value is less than end index's value.

Or I also can think about the alternative idea. It is to iterate the start position from i = 0 to 4,

i = 0, the rectanlge is 2 + 2 + 2 + 2 + 2 = 10.
i = 1, the rectangle is 4 + 4 + 4 = 12.
i = 2, the rectangle is 6.
i = 3, the rectangle is 5
i = 4, the rectangle is 3

Being interviewer: Leetcode 250: Count univalue subtrees

April 5, 2018

Introduction

It is my favorite algorithm in March, 2018. I had two practices on this algorithm, one is to write the algorithm in 30 minutes mock interview, and the second one is to review the peer's practice. I chose the algorithm to interview the peer on April 4, 2018 10:00 PM, but I could not give out the solution based on the peer's code.

Follow up 

Here is the code I reviewed in mock interview. The peer asked my advice, but I could not tell at that time the code was bug free.

Now it is 9:20 PM April 5, 2018, I like to write a C# solution based on the simple idea, using negative to represent that the tree does not have same value. Here is my C# code.

2,000 Things You Should Know About C#

April 4, 2018

Introduction

I was asked in my mock interview as an interviewer a few days ago, what language I will use in mock interview. Python, Java, JavaScript are mainly choices. I chose to use C# language.

In order to learn C# better, I spent a few hours in the morning to go over items in basics catalog on 2,000 Things You Should Know About C#.

C# reading 

Here are the items I plan to study again. I like to learn C# even I am very busy. Just work on 2,000 things, work on a few items every day.

• #732 – Destruction vs. Collection
• #733 – How to Tell If an Object Has Been Garbage Collected
• #734 – Accessing the Original Object Referenced through a WeakReference
• #735 – Don’t Trust WeakReference.IsAlive If It Returns true
• #736 – Target of a WeakReference Will Be null after Garbage Collection
• #738 – You Shouldn’t Explicitly Force Garbage Collection
• #740 – Short vs. Long Weak References
• #771 – Summary of System.Object Members
• #803 – Situations When You Might Use the var Keyword
• #804 – Tradeoffs when Using the var Keyword
• #805 – An Example of Discretionary Use of the var Keyword
• #806 – An Example of Mandatory Use of the var Keyword
• #846 – A Call Stack Keeps Track of Methods that Have Been Called
• #847 – How the Call Stack Works
• #921 – Objects Are Explicitly Created but Automatically Destroyed
• #922 – Ways in Which References to an Object Are Released

Pluralsight.com: Adobe muse building responsive single page website

April 4, 2018

Introduction

It is time for me to spend two hours to work on the course called: Adobe muse building responsive single page website.

Being interviewer: Leetcode 54: Spiral matrix print

April 4, 2018

Introduction

It is the algorithm for me to give the mock interviewee to work on back to Feb. 14, 2018. I just noticed that the interviewee joined the top software company MTN recently. So I spent time to replay the video and also wrote a C# practice based on his practice. It is very easy to tell from the video that the peer had very good problem solving skills.

Code review

Here is Java practice code I reviewed. I like to practice it using C# as well.

Feedback I gave

Here is the feedback I gave out on Feb. 14, 2018 after the mock interview. 

Leetcode 282: Expression Add Operators

April 3, 2018

Introduction

It is hard level algorithm. I like to study the algorithm so I searched the discussion panel. I found one link with very good comment, here is the link.

Code study

I like to prepare an algorithm for my 10:00 PM mock interview as an interviewer. I like to try a new algorithm, and also I like to learn quickly through the mock interview as well. Now it is 9:29 PM.

First, I have to understand how to handle multiplication. Here is the link to give out the explanation.

If you want to add a * between 3 and 4, you would take 3 as the digit to be multiplied, so you want to take it out from the existing eval. You have 1 + 2 + 3 * 4 and the eval now is (1 + 2 + 3) - 3 + (3 * 4).

Pluralsight.com: Building angularJS and node.js apps with the MEAN stack

April 3, 2018

Introduction

I plan to spend 4 hours to study the course called Building angularJS and node.js apps with the MEAN stack.

Leetcode 76: Minimum windows substring

April 3, 2018

Introduction

It is the hard level algorithm. I have practiced similar algorithm on mock interview platform over 5 times last 12 months.

Code review

Here is C# practice I did based on one of discussion.

Leetcode 587 Erect the fence

April 3, 2018

Introduction

It is hard level algorithm related to sweep line algorithm. I plan to work on this algorithm called Erect the fence.

Being interviewer: Leetcode 56: Merge intervals

April 2, 2018

Introduction

It is my mock interview's algorithm called Leetcode 56: Merge intervals. I asked the peer to work on the algorithm by mistake, I like to ask him to work on Meeting Room II.

Algorithm analysis

The peer worked very hard and he gave his analysis for the algorithm. Here is the analysis.

One thing I really like to share is that the peer can write the perfect analysis without any issue in his writing.

The reason the peer can pass code screen and get phone screen of Google, I believe that he definitely has very good analytical skills.

Being an interviewer: BST successor search

April 2, 2018

Introduction

It was my 10:00 PM mock interview. I had chance to discuss with the peer about his algorithm BST successor search. He wrote the program using JavaScript.

We spent extra time to discuss the algorithm, and we ended up the discussion around 12:40 AM. I spent 2 hours 40 minutes discussion with the peer. The peer is very talent and he is preparing Google phone screen.

I like that the peer can write very clearly for the algorithm analysis. This is the first time I worked with a peer to write so clearly and also very accurate.

Code review 

I also helped to review the peer's Javascript code. I also learned a few things about JavaScript.

Leetcode 253: Meeting room II

April 2, 2018

Introduction

It is 10:00 PM mock interview. I had chance to work on Sudoku solver. And after the mock interview, I had discussion with the peer about algorithms Meeting room II.

We had discussion about the algorithm around 20 minutes.

Algorithm analysis

Here is the analysis the peer gave in mock interview.

I also like to follow up after mock interview, I found similar idea in Leetcode discussion. Here is the link.

Follow up 

April 3, 2018

I reviewed the code written in C# language using line sweep algorithm. Here is the C# practice.

Also I like to read the book chapter 30: Sweep line algorithms. I did first time to learn the algorithm called Andrew's algorithm, also called Andrew's monotone chain convex hull algorithm. I also found a hard level algorithm to practice and apply the Andrew's algorithm, which is called Leetcode 587 Erect the fence.

Sudoku solver

April 2, 2018

Introduction

It is such great experience to work on Sudoku solver in mock interview. I wrote the algorithm in less than 30 minutes.

Code review

Here is my analysis with C# code.

Leetcode 277: Find the celebrity

April 1, 2018

Plan to work on the algorithm Leetcode 277: Find the celebrity. Let me think about 10 - 15 minutes first.

Leetcode 261: Graph valid tree

April 1, 2018

Introduction

I like to read a few blogs about Leetcode 261: Graph valid tree.

Leetcode 151: reverse words in a string

April 1, 2018

Plan to read discussion panel and vote 10 ideas.

Leetcode 139: Word break

April 1, 2018

I am planning to study Leetcode 139: word break algorithm again. I like to read discussion panel and vote at least 3 ideas.

How to be a good interviewer?

April 1, 2018

Introduction

I like to do a small research how to be a good interviewer. I learn to be an interviewer by myself, I got a bad feedback when I mock interviewed a person anonymously no video from Singapore with over 6 years experience a few days ago. I gave the algorithm called Leetcode 152: Maximum subarray product. Because I did not want to give all hints out to solve the problem, the interviewee wrote an idea with so buggy code using checking negative elements. At the end of 45 minutes, both of us did not learn anything. The interviewee did not learn anything from the mock interview, I also got bad feedback.

So in order to make mock interview learning experience, I choose to give out all hints and sometimes I make it a tutoring session.

Deletion distance

On March 31, 2018, I gave the peer a mock interview using deletion distance. So I decided to step in and worked on the algorithm together, discussed how to approach the dynamic programming algorithm together.

Being interviewee: Island count

March 30, 2018

Introduction

It is my mock interview algorithm at 12:00 PM. I spent 17 minutes to write the algorithm. I learned a few lessons through the mock interview.

Mock interview performance

I was lazy and do not declare two variables visitRow and visitCol, and then I mix startRow with visiitRow, startCol with visitCol. I wrote the code and forgot to push four neighbors into queue, I pushed startRow, startCol to the queue instead.

I fixed the issue when I did white board testing. I finished the coding in less than 17 minutes, and I failed 3 test cases. It took me one minute to find the bug from line 47 to line 50. I fixed it in less than one minute.

Next time it is important to declare new variables for visitRow, visitCol, otherwise I may mix things together. Build a good habit.

Here is my C# code.

Here is my last practice five days ago.

I enjoy to write code using BFS and also using queue. It is fun and it is easy to make mistakes. But with more practice, I will be more comfortable to think using BFS.

Yichun city house research

March 30, 2018

Introduction

It is not too hard to do research on house market in the city of Yichun, my home town. As a software programmer, I have to learn to apply my research ability in data structure and algorithm to a real world.

One of my projects is to find a small condo to purchase when I take a vacation back to China from April 12 to April 18.

Here is the project near the place I grow up, my sisters living there are physicians and teachers.

$20,000 Canadian dollar 1 bedroom/ 1 bath condo

I like to look into pengshen gold collar condo. Here is the website link.

Saturday 10:00 AM mock interview

March 30, 2018

Introduction

Life is tough. The first time I met a peer from New York, he setup his laptop inside the car and then we had a short discussion about mock interview. It is his first mock interview. He told me that he mainly worked on Java, he is looking for a job. He does not have interesting in algorithm and data structure. He worked on a few startups before.

I was told to work on my algorithm first. I spent five minutes to explain the idea how to solve recursive problem called minimum sales path. How to think about recursively? Explain the root node, check its value, and if there are no children, then return its value; otherwise get all its children, ask them to solve the problem, and get the minimum value from those paths.

The peer asked me how often I solve the problem. Do I do other things? I explained a few things:

// leetcode - hackerrank contest /
// stackexchange.com /
// frontendmasters.com - take courses -
// pluralsight.com - 4700 courses -
// C# - html, css, jquery, javascript, at work - learn new technology - angular JS - react framework,

My review for the peer

The video was cut after 15 minutes. I chose not to write any code, I just used my own words to explain the algorithm first. And then we had short discussion about the algorithm and how to learn things in general.

I left the feedback. I wrote in less than 5 minutes.

I was touched by your hard working spirit. Please do not get frustrated to look for a job, specially a programmer job. I used to work in USA with different jobs and experienced difference emotions as a software programmer, student. 

I think that it is good decision to go back to study data structure and algorithm foundation. It also helps me to focus on the foundation. If you like to learn how to do problem solving, in data structure and algorithm, and know how people work hard on that. You will find that the job you are doing, looking for doing is much easy compared to this part. 

You set up everything working inside the car for the mock interview and sit in the driver seat. That is so amazing. 

Trust hard word. Word hard. I write coding blog to encourage others to work hard. Do not get frustrated. 

http://juliachencoding.blogspot.ca/

Actionable Items

As a software programmer, I learn to respect people around me how hard they are working. If you do like to be a software programmer, you have to sacrifice and learn how to work with people. Help them make money. 

As we know, there are high pay jobs from top software companies, we as a software engineer can work hard for. But we all know that it is so hard to achieve, most of us cannot make it. 

We have to think about more how to make money outside the job, and then stay in software engineering field and keep doing our loved jobs as a programmer. Love the job you are working on, try to bring in more things to your career; enrich your own life with hard work. 

Find pairs and keep the order specified by the original array

March 30, 2018

Introduction

It is my mock interview algorithm. I wrote a solution but I did not meet the requirement of specified order. I need to rewrite another one after mock interview.

Code review

Here is the C# practice I wrote in mock interview.

Being interviewer: Deletion distance

March 29, 2018

Introduction

It is the dynamic programming algorithm called deletion distance. I had a 12:00 PM mock interview. I had chance to discuss with the peer how to solve the problem by playing with dynamic programming table.

How to build a dynamic programming table?

Here are a few things we discussed.

1. How to define rows and columns?
2. Add "" string for row and column
3. First time I found out that I need to add extra row/ column to identify current char to work on.
Line 19 is extra row added to show current char to work on, first char next to line 23 to line 26 is the extra column added to show current char to work on in another string.

4. I worked on the first row and first column, and then I did write line 29 to line 33 to explain the recurrence formula.

5. I asked the peer to work on the second row. He worked on second row and third row, he made a mistake to calculate distance("fro", "do"). And then I asked him to check diagonal value dist("fr","d") = 3.

We then had discussion how to prove that the minimum distance is the diagonal value when the current char is the same as the other string's current char.

The proof is from line 25 to line 36. I explained that the matrix or dynamic programming two dimension table from left to right, top to down, it is not descending order. So it is easy to prove that based on the fact.

Giving advice

I also wrote some advice for senior developers to pick up algorithm and data structure in general, specially on deletion distance algorithm:

Do not feel frustrated. I also make a lot of mistakes and practice a lot of times on this algorithm. Practice more. Learn one thing a time.

I do not need to find out how good you can write code. Try to play with setting up a two dimensional table first, and then write code based on the steps. It may take a few times. Once you get a lot of practice, dynamic programming should be very mathematical, use a template, it is easy to write the code.

Being an interviewer: Pancake sort

March 29, 2018

Introduction

It is my interesting thing to learn how to be a good interviewer. Since I was so patient and also gave some advice like "write readable code" and "write simple code", I ended up knowing that a very competitive programmer with so many medals on hackerrank, and my favorite codeforce.com, the expert competitor.

Code review

Here is the C++ code I reviewed. Most of time the peer worked on the problem related to const in C++. The flip function change cannot be done in place, we debugged the code and found the issue.

Being interviewee: Array of array products

March 29, 2018

Introduction

It is my algorithm to write in the mock interview. I remembered that I have to work on one multiplication from left to right iteration using dynamic programming, and then two multiplications from right to left calculation.

I have to learn again to write a correct solution in less than 10 minutes. This time I spent 18 minutes, and also I got a hint from the peer. The peer told me to define a variable leftToRight to save product of array elements on line 18, and also switch the order of line 22 and 24 to assign the value first, and then do the multiplication next.

Code review

Here is my C# practice.

Being interviewee: Leetcode 10: regular expression matching

March 29, 2018

Introduction

It is my sick day. I have to stay at home. Yesterday I noticed that my nose was running and made sneeze, one of coworkers asked me if I was sick. I told her that I had allergic. But I had to honestly admit that I had a cold, I could not go to work and stay at home.

I had 10:00 AM mock interview, I had to work on Leetcode 10: regular expression matching algorithm. I spent 34 minutes to write analysis and code, I fixed a few bugs to pass all test cases.

Code review

Here is my analysis and C# code.

I like to write down my misunderstanding in my first writing, and then how I fixed the bug through the white box testing and web compiler.

For example, to build a dynamic programming table, I have to work on "b", "b*".

                    ""  "b"   "*"
                    ""  "b"   "b*"  - pattern
              --------------------
""    ""         T     F      T
"b" "b"        F     T      T

In order to calculate dp[row, col], I need to find the text char and pattern char first, and then work on current char only.

Highlights of bug fix after first writing in mock interview:

1. I did white box testing, need to fix the bug using test case "" matches pattern string "a*b*". I added line 21 to line 33.
2. web compiler runs the test cases. I failed most of test cases.
I noticed that I could not memorize the solution. I need to work on the solution itself.
I fixed line 25 checking pChar == '*' instead of checking pChar and its next char.
3. line 40, check pChar is '*' instead of checking next char is '*'.
4. line 46, col - 1 instead of col - 2 which causes index out of range error.

Dynamic programming quote

Today's quote on dynamic programming. I think that I learn something from today's practice.

Work on dynamic programming, do not worry about next char. Work on current char only. 

Best medicine to cure my cold

Here is the feedback I got from the peer. It helps me to recover from my cold. Actually the peer is very competitive programmer on codeforece.com, expert with contest rating: 17xxx ( max: expert, 1886), competitive, also on hackerrank.com with 5 gold medal.

One more practice

I knew that I was sick with a cold, and then I felt some nervous in mock interview. It is hard to write a dynamic programming solution in less than 30 minutes.

I knew that something will go wrong. To learn a hard level algorithm, I have to be so patient and let myself make mistake first; and then find the ways to fix it in mock interview, and also in less than 30 minutes.

First of all, I mixed the dynamic programming solution with recursive solution. Since my last practice I spent over 40 minutes to write a recursive solution in mock interview to play with a friend less than one month ago. I look ahead for star pattern, current char is a - z, I check if next char is star. But it is wrong to do that in dynamic programming, mix current problem with next problem.

Dynamic programming is to work on the current problem and use subproblems cache results.

Sick day

March 29, 2018

Introduction

It is my sick day. I have not had a cold long time. Usually I play a lot of hours tennis sports and swimming, I stay healthy. But this time I got my nose running, and then I have to call a sick day, stay at home, plan to do something to help me recover.

Sick day Thursday

I need to find ideas to recover quickly.

Natural flu treatment: 9 proven flue busters.

Yichun city real estate research

March 29, 2018

Introduction

It is the learning experience to be a responsible adult. I like a lot of things, like shopping, clothing, but somehow I do not spend enough time to do research on the city I grow up called Yichun city.

Year 2007

I spent over one month to stay in the city of Yichun, at that time, I was young and naive. I knew that life is not easy. I lived with my mom and my sister and stayed in a home near the center of the city. At that time, my sister is a teacher of Yichun university. I learned something from her since she works full time as a teacher. She never needs to worry about job security, visa status and American dream.

At that time, she argued with me that the home price will not go up since cross street high-rise building $1000 RMB/ square meter.

At that my 401 K in USA can afford to buy two 2 bedroom condos in 2007. I was not satisfied but I did not purchase anything in my hometown. Now it is $3000 - $8000 RMB/ square meter.

After 10 years, my 401 K do not do very well, since I sold everything in high risk fund and changed to stable fund in 15 years low back in 2009.

Real estate research

It is time for me to do some research. Always stay positive. Keep good faith on what I have. No matter how little I have, try to use it as bible teaching.

Hebrews 13:5

Keep your lives free from the love of money and be content with what you have, because God has said, “Never will I leave you; never will I forsake you.”

Being an interviewer: Root of a number

March 28, 2018

Introduction

It is a binary search algorithm called root of a number. The hint I gave in the mock interview as an interviewer is to explain how many numbers to search for x = 8, n = 3, it is from 0, incremented by 0.001 to 8, total is 8000 numbers to search.

Binary search algorithm

Here is the binary search algorithm I reviewed written by the peer. The algorithm still has issues to pass a few test cases. I like to look into as well.

I like to get organized and review all my past practice.

Code review

Actually the code should be updated in two places:
1. Line 44 and 45, return (double) m/ 1000;
2. Line 56, return (double) s/ 1000;

The argument is that when s == e on line 37, the return value should be s, not -1 or 0.0.

Incremental value 

It is better to change the design, and use 0.0001 as a different number to apply binary search. Here is C# code.

Given the example x = 8, n = 3, instead of search 8000 numbers, we choose to search 80,000 using binary search. Incremental value is 0.0001 instead of 0.001.

Being an interviewer, it takes some time to figure out how to guide the peer to lead the optimal solution and pass all test cases.

Work count practice

March 28, 2018

Introduction

It is very challenge algorithm to work on in 30 minutes. I have worked on the algorithm more than 6 times, but I never had chance to complete the code and pass all test cases in less than 30 minutes.

Today I also read the problem statement, I need to write code to keep the original order of words in the same bucket.

Code practice

Here is the C# code I wrote in 30 minutes in the mock interview. After the mock interview, I spent at least 30 minutes to complete the code and pass all test cases. Here is the C# code to pass all test cases.

Here are highlights of my work after mock interview:

1. line 18, Punctuation chars: "., !:;?", I missed :, ;, ?
2. line 22, Add function argument totalCount
3. line 22, function argument should be replaced, not orignal string document.
4. line 27 - line 41, I fail to call string.Replace to replace ' using empty char, so replaceChar function is written.
5. comment out line 16
6. Still confuse ToLower() function call, should string.ToLower() or document.ToLower()
Argument: string is class, not an interface, so ToLower is member function of string class, not interface member function.
7, line 57 and line 58, index variable should be used instead of using variable i defined on line 49.

2,000 Things You Should Know About C#

March 28, 2018

Introduction

It is time for me to slow down to practice data structure and algorithm, and think about how to advance myself as  a C# programmer. One thing I like to do is to learn something quickly. I spent over one hour today to study interface from 2,000 things you should know about C#.

Interface

#434 – Interfaces

#435 – Implementing an Interface

#436 – The Implementation of an Interface Can Be a Subset of the Class

#437 – Access Interface Members through an Interface Variable

#438 – Benefits of Using Interfaces

#440 – A Class Can Implement More than One Interface

#441 – Implementing Interface Members Explicitly

#442 – Explicit Interface Implementation Allows Duplicate Member Names

#443 – An Interface Cannot Contain Fields

#444 – Interfaces Can Inherit from Other Interfaces

#445 – Differences Between an Interface and an Abstract Class

#446 – Deciding Between an Abstract Class and an Interface

#447 – Use as Operator to Get At an Object’s Interfaces

#448 – Use the is Operator to See if an Object Implements an Interface

#449 – You Can Pass an Interface Variable to a Method

#450 – Interfaces Should Normally Start with the Letter ‘I’

#451 – Implement Interface Explicitly to Simplify How a Class Appears to Clients

#454 – Return an Interface as a Return Value from a Method

#455 – Define an Interface Based on Existing Members of a Class

#456 – Explicitly Implemented Interface Members Are Automatically Private

#536 – Using a Generic Interface

#537 – Implement a Generic Interface with a Generic Class

#612 – Members of an Interface Are Implicitly Public

#613 – Interfaces Cannot Contain Static Members

#647 – A struct Can Implement an Interface

#799 – Interface Members Are Implicitly Public

#1,067 – Covariance and Generic Interfaces

#1,068 – Generic IEnumerable Interface Is Covariant

#1,069 – Contravariance and Generic Interfaces

It will take me 2 hours to go over those items.

Book reading: Competitive Programmer's Handbook

March 27, 2018

Introduction

It is my 10:00 pm mock interview as an interviewer. I never expected that I will interview a senior who will prepare Google onsite in 3 weeks. So I did ask two algorithms I studied today, and then I was so surprised to learn how good the peer gave his analysis, and also I learned the algorithm from his analysis.

I was told to read the book called: Competitive programmer's handbook by Antti Laaksoen, Draft December 10, 2017.

Advice from the peer

1. read Competitive Programmer's Handbook

2. 200+ on leetcode  - top 100 question

2.1 strong at DP - don't have to solve every DP

2.2 graphs -> open that topic and solve medium and hards

3. 10 minutes to solve a question -> look up the best solution for this problem -> don't code it immediately -> wait 2-3 days at least

Sort k shifted array

March 27, 2018

Introduction

It is the sort algorithm and I cannot use heap since C# does not have class. I write a function to find the minimum index in K + 1 contiguous subarray.

Algorithm practice

Here is my C# practice.

Leetcode 745. Prefix and Suffix Search

March 27, 2018

Plan to work on this hard level algorithm Leetcode 745: Prefix and suffix search.

Leetcode 211. Add and Search Word - Data structure design

March 27, 2018

I am planning to work on this medium level algorithm in short future. I like to work on the algorithm and think about 10 - 15 minutes first.

Leetcode 152: Maximum product subarray

March 27, 2018

Introduction

I like to work on this algorithm Leetcode 152: Maximum product subarray, and I find that it is similar to the algorithm I practice so many times called float numbers and operators.

Algorithm practice as an interviewer

I chose the algorithm to interview the peer in mock interview. The peer is very talent programmer, he had a facebook onsite last December, and he prepares for Google onsite. what I found out is that he needs some hint to come out dynamic programming solution, but his coding ability is very strong, and also the analysis ability.

Here is the transcript.

Facebook interview algorithms

March 27, 2018

Introduction

There is very organized folder on the github with over 70 algorithms. I plan to study those algorithms one by one. Here is the link. The title is called facebook interview algorithms. The author studied those algorithm to prepare facebook intern from August 2016 to March 2017, and the source is from 1point3acres.com.

70 algorithms

I plan to work on over 70 facebook interview algorithms. That is a lot of algorithms to work on.

I learn from my mock interview experience, only 30 algorithms. I have practiced those 30 algorithm over 7 rounds.

Being interviewer: Leetcode 253: Meeting rooms II

March 27, 2018

Introduction

It is a medium level algorithm. I spent over 30 minutes to read a few blogs related to the algorithm. I feel that it is very interesting algorithm, I like to spend more time and write the algorithm as well.

Algorithm study

It is so much fun to study the algorithm. There are a few solutions but Leetcode does not have public discussion for the algorithm. So I like to practice a few solutions.

Actionable Items

I asked the question on the mock interview on March 27, 2018 10:00 PM. The peer gave me the solution and I was told to work on line sweep algorithm. Here is the analysis.

I just could not believe that the peer worked on the algorithm before, but he has very good understanding of the algorithm.

Find two items with given sum in the array

March 26, 2018

Introduction

It is another 10:00 PM mock interview. I do not pay special attention, but I got a review about things to work on. I think that the feedback is very helpful, so I like to share here.

Code practice

Here is my C# code practice.

Here is my feedback. I need to learn to speak slowly.

Being an interviewer: Leetcode 250: Count univalue subtrees

March 26, 2018

Introduction

I like to learn to be a good code reviewer. Sometimes I practice with a friend a few times, I start to learn how to help the peer to give some code review.

Code review

I spent over 60 minutes to work on the algorithm, the peer gave me very good advice how to make improvement. So I also like to work hard and give some code review.

I will document my code review here as well.


Here is the Java code I got from the peer and then I cleaned up test cases and analysis of the algorithm.

Here is my code review:

isUnivalTree function

You can simplify the function isUnivalTree using one statement, please see attached image of the highlight of your code:

Here is my advise how to write in one statement instead. I will explain why I like to do that.

The argument is this, left && right is not true, you do not need to check root value compared to left child value if there is one. So your logic includes redundant work. 

checkSize function

There are a few issues on checkSize API,

1. First the return type does not match API definition, people will surprise to get a return Node when the function name is called checkSize. You should return size instead of a Node. Why we need a Node, where to find the size in the Node object. 

Also the function name checkSize is not meaningful, it is better to call calculateUnivalSubtreeCount. 

2. Second, you have a giant expression I circled using red color. It is better to avoid negative checking. Think about default value, and then write a positive checking. 

  Here is the code I think with better presentation:

Clean up is a small good thing to do

I also like to point out that it is good habit to clean up document before sharing with others. Remove extra space, unrelated comment, and make the code clean and readable. Once you do it in every mock interview, you will start to learn how to act quickly. You will apply the habit to the work and also in the official interview.

Working hard does not mean staying up 1 AM or 2 AM. It takes time to build up good knowledge of data structure and algorithm. But builing a good habit just takes determination and good mind of making smart choice, that is my thinking. Hopefully I can bring your attention to the issue.

Leetcode 765. Couples Holding Hands

March 26, 2018

Introduction

I like to work on this hard level algorithm called Leetcode 765: Couples holding hands.

Leetcode 41: Find missing positive

March 26, 2018

Introduction

I like to get organized on those mock interview algorithm. One algorithm is called Find first nonnegative integer in the array, I went over the practice and added the label. Also I found out that I need to work on the hard level algorithm Leetcode 41: Find missing positive.

It is my idea to practice 10 ideas based on Leetcode discussion in order to learn a hard level algorithm.

Find first missing nonnegative number

March 26, 2018

Introduction

It is the algorithm to find first missing nonnegative number in the array. What I like the algorithm is to work with the constraint. The constraint is that the array cannot be modified, and then second algorithm is to modify the array.

Code review

I like to work on the algorithm one more time. Here is my C# practice for the first solution without changing the input array. And here is the second solution to change the input array.

Actionable Items

Google and find algorithms in Leetcode related to the algorithm.

Being interviewer: Longest Arithmetic Progression Algorithm

March 26, 2018

Introduction

I like to learn the algorithm by asking the interviewee to solve the problem. I had a mock interview on March 25, 2018, so I had chance to work on the algorithm over 30 minutes.

Mock interview

Here is the mock interview discussion I had with the peer.

Leetcode 250: Count univalue subtrees

March 26, 2018

Introduction

It is a medium level algorithm. I was asked to solve the algorithm in the mock on March 25, 2018. So I had chance to learn from the peer.

Code review 

Here is my C# code. I got the idea to solve the problem since I studied another tree algorithm
Leetcode 230. Kth Smallest Element in a BST on March 23, 2018.

Being interviewee: Leetcode 250: Count univalue subtrees

March 26, 2018

Introduction

It was my algorithm called Leetcode 250: Count univalue subtrees.

My practice

First I was asked to work on the function to check if binary tree has same value. And then I was told to work on the algorithm to count univalue subtrees.

Here is my practice.

I came out the working solutions for both algorithms. But the first one the peer told me to simplify the algorithm. I do not need to use extra two arguments: hasDefaultValue, defaultValue.

I spent 28 minutes from 9:18 PM to 9:46pm to work on the first algorithm, including discussion with the peer. And I spent 41 minutes to work on the second algorithm, and also had a discussion with the peer on different test cases.

Yichun city - my home town

March 25, 2018

Introduction

It is my Sunday afternoon research. I need to find something to work on related to my China vacation trip. I only have 8 days trip include one round trip more than 22 hours on the plane. I budget to spend $800 Yuan on fastest train round trip from Shanghai to Yichun to visit my family in the city of Yichun.

House research

I could not believe that I could not afford more than 40 square meter place to purchase. I like to find a place to purchase so that I can do some business in my life as an educator in my own home town. I like to do something if I like to do it.

Here is the article I like to read about the city of Yichun.

One more research

Here is something I like to study. The cost to do the work inside the home.

Island count

March 25, 2018

Introduction

It is my mock interview algorithm called Island count. I was so excited to work with a peer who is from Israel this morning 10:00 AM. The peer told me that it is better to write an iterative solution.

Code review

I had to follow the advise from the peer, and then I decided to write a queue to apply breadth first search to visit neighbors, mark visited.

Here is my C# code passing all test cases.

The instruction to play mock interview nicely

I have worked on this algorithm so many times. I know how to train myself one more time nice and easy, get more experience how to write readable code, practice one more time to explain the algorithm and talk about ideas with a peer.

First few minutes, I will write down the matrix using example 5 x 5 matrix, and go over row by row from left to right starting from position (0, 0). If I find the first one, I will mark it visited, and then use DFS/ BFS to visit all neighbors as elements in the same island. I will increment island count variable one. I will mark the first island using char 'A', next island using 'B', likewise. I will apply the same analysis twice, using -1 to mark first two islands A and B, and then just quickly apply C, D, E, F for the rest of islands.

After that, I will ask the peer's advice to choose DFS or BFS. Give him/ her a choice, and follow  the advice. I am willing to write any solution, but I do not want to stick on one solution, I like to practice any solution if need.

This time the peer told me that I should not use recursive function, it is written to write iterative solution in mock interview platform for interviewer. So I have to follow the advice, decide to write the iterative solution.

I thought about using for loops, and then decided to write a queue. Since it is the only way I can apply BFS without using recursive function, otherwise I cannot handle the neighbors just using loops. Data structure queue is definitely needed.

Beautiful code

It is not tough for me to write readable code using Queue, and apply BFS algorithm. I have practiced similar algorithm so many times last 12 months.

I learn how to write readable code last 18 months.

Give credit to the code reviewer, here is the link.

Here is the blog about my past practice. I need to get organized and then I can review what each my past practice and see how good I am getting.

Road trip to Vancouver island

March 25, 2018

Introduction

I got an invitation to have a road trip to Vancouver island with my two classmates back in Shanghai Jiaotong university from 1984 to 1988, the trip was on Sunday from 7:00 Am to 6:00 PM from the city of Surrey to Vancouver island Victoria, Butcher garden.

Here is the instagram link.

China trip from April 12 to April 18, 2018

March 25, 2018

Introduction

It is time for me to write something for my coming China trip from April 12, 2018 to April 18, 2018. It is so difficult for me to make a decision, the get-together of Shanghai Jiaotong university applied math major class from 1984 to 1988. 70141 is the name of class for around 30 students at that time.

How to make a decision for the trip?

I had two classmates who will fly from USA and Canada to Shanghai on April 12, 2018. One of my classmate who is a PH.D. graduate from California, I have not seen her over 30 years, she asked me why I could not join the meetup.

I checked the calendar and also airline ticket by Air Canada, 12 hours direct flight, from April 12 to April 15 is $570 Canadian dollars. No matter what happens, I should be able to take April 12 Thursday off, Friday off, and then come back next Monday. Later, I decide to take two more extra days since the ticket price is same until Wednesday April 18. After April 18, the airline ticket is above $850 Canadian dollars.

How to plan for the China vacation only for 8 days? 

What makes one person success financially?

March 25, 2018

Introduction

I graduated from top university from China called Shanghai Jiaotong university. When we were in the second year, 1985, there is a new classmate who joined us, his name is Neil Sheng, now he is top 100 ranking richest people in China. I had so many successful stories to tell from my classmates or friends back in Shanghai Jiaotong University or Florida Atlantic university.

It is fun to write a small research topic and spend some time to think about. Life is such a great teacher. If you treat your neighbor, friends, classmate nice, you will have so many lessons to learn as an adult. I will share my person stories and will make this Sunday more meaningful.

What makes one person successful financially?

I have five siblings, and also I was told so many stories from my siblings. How hard they work as a teacher, physician, or a small business owner.

I have friends to visit me from California, the young successful couple both with Ph.D. degree, they visited my home in the city of Vancouver in 2017. And she told me that she got 3 offers in one month in California. I was so surprised that the huge difference in the corporate world later on.

Last week I had a friend who visited me as well. She told me another successful story. She chose to stay in Shanghai and had a very successful career, and took care of her parents last 20 years. And she shared with me a story about how good it is to obey your parents and respect your parents, give back to your parents, similar to Christian testimony. Since she is a good daughter and she likes to take care of aging parents, she bought a home over 15 years ago to let her parents living close to her. She does not like to stay in the same house with parents. That one good deed helps us to gain over 5 million Chinese dollars alone in the capital gain over 15 years.

I offered her a road trip to visit the city of Seattle since I plan to have a vacation to Seattle. I did drive her in 2007 from New York to Boston, and we visited Yale, Harvard and MIT universities. At that time, she was planning to find a university for her daughter.

Struggle is fun and meaningful

Ephesians 6:2 Honor your mother and father.

Being interviewer: Sudoku solver

March 25, 2018

Introduction

It is such great experience to work with a software engineer from Israel 10:00 am mock interview.  The peer also told me that she works for one of top four software company in the world. She worked on Sudoku solver.

As an interviewer, I like to write down some highlights for my code review.

Code review

Here is the solution I reviewed. First of all, the peer wrote down the analysis very clearly and asked me if I followed her idea after she wrote some of the code from line 21 to 44. After she wrote the solution to call recursive for next iteration, she asked me the feedback.

Highlights of my code review:

1. line 25 to line 26, I added those two lines. I explained that there is a bug to find next position of '.' char. Line 23, I changed column = j to column = 0, and add line 25 and line 26 to start from (i, j).

2. line 56, I explained to the peer that no need to check, HashSet.Remove can handle the case if the char is not in hashset.

3. line 88 to 91, I explained to the peer why backtracking is necessary. Her argument is that next iteration the element will be replaced by the available number. And then I gave her the example, first row with first two elements 5 and 3, and 3 empty space with '.', if we work on the third '.' and try the last available number but fails, we need to put '.' back and then continue to work on second '.'. Recover the original status.

Using graph like the following:
5 3 _  _   _
              _ fail ->'.', work on third dot, (0, 4)
          next iteration to work on second '.'

4. work on nextRow and nextCol calculation. Originally the peer wrote (emptyRow + 1)% n, (emptyColumn + 1) %m,

Actionable Items

It is very good to work with the peer on this algorithm. Today is Sunday. I choose to stay at home and work on mock interview. Yesterday I spent over 90 minutes to work with a peer on budget cap calculation. Later I talked to my roommate Emma, she told me that I have to think for other people. If I meet  a strong player on algorithm and data structure, I will talk over 90 minutes. Think about the other way, same applies to the peer I met as well.

Emma is a very good IELTS teacher, and she told me to work on cleaning the living room table together. What I did is to learn and stay organized. We both laughed about the shopping I did in Seattle, and I did make a mistake to purchase too many Nike shoes for myself. I bought 3 pairs of Nike shoes, one pair I wore two days, it broke my skin near my ankle. I went to Seattle with my friend from Shanghai, she laughed about me how I can wear 3 pairs of sneakers. It turned out not cheap for 3 pairs of shoes, $150 Canadian dollars.

Leetcode 734: Sentence similarity

March 24, 2018

Plan to work on the algorithm called Sentence similarity, easy level question. I like to study the blog related to this algorithm, the link is here.

Being interviewer: Find new cap value

March 24, 2018

Introduction

It is my favorite algorithm to find the cap value to fit into new budget. Today I also had chance to share the idea how to solve the problem using depth first search, dynamic programming method. Also it is so interesting to learn from the peer's failure. His idea is to use average function to determine the cap value, which failed two test cases.

Algorithm analysis

It is the learning experience for me to share the idea how to solve the problem. I like to learn the algorithm very well, one way to do it is to go through the experience as an interviewee. Find out what kind of concern the peer has, and help him to develop a solution in less than 60 minutes.

I was very patient and spent extra 30 minutes to stay in the interview.

Here is the analysis between two peers in mock interview 12:00 PM.