Code review: Array quadruplet

April 30, 2018

Introduction

It is so happy for me to continue to practice Array quadruplet algorithm since last March. What I have learned through over 10 rounds mock interview is that I have to continue to learn the algorithm through each practice.

It is the big surprise when I chose the algorithm to ask the peer last Saturday 10:00 PM mock interview. I tried to test a senior in the university how good he is since he told me that he had ICPC contest experience in high school.

Build a hashmap on the fly

I like to answer my own question asked five months ago on stackexchange.com. Here is the question's link. Here is my answer's link.

Leetcode 4 sum discussion panel

I have to push myself to learn from others. One drill is to read as many discussion as possible, and try to figure out new ideas, creative thinking process. I spent 30 minutes to read through the discussion, and also wrote a reply. Here is my reply link.

I noticed that I had some issues, since I keep checking code review my answer link. I know that it is waste of my time. I should spend time to read more discussion on Leetcode 4 sum.

Sometimes I notice that I have to push myself to show concern to others, people in the community, and also give out support for other people's good thoughts and work they share.

To be selfish or pessimistic, it is not working very well in this fast-paced software industry. This is the first time I make this argument.


Here is my post to show my idea and answer for Leetcode 18: 4 sum. I did spend 30 minutes to read my submission eleven months ago and then I decided to write a new solution based on my practice on array quadruplet.

One step further

Here is the reply I gave to the most view answer 6.1 K views. I shared the tip to lower down the time complexity to O(n * n).

Being interviewer: Array quadruplet

April 29, 2018

Introduction

I had a mock interview with a young undergraduate student with ICPC contest experience. So I like to ask him to solve my favorite algorithm Array quadruplet. I think that he did one on dynamic programming, and then I tried to evaluate how good he is.

Biggest surprise was that he gave me the solution I could not understand. And then I asked him a few question, ask him to explain using example. He did perfect job to explain the algorithm.

It turned out the algorithm is optimal solution. I like to post the answer for my own question asked more than 6 months ago. Here is my question link.

Mock interview

Here is the algorithm the peer wrote. At the end of interview, I asked him to connect to linkedin, it turned out that he worked for facebook as an intern already.

I could not believe that my mock interview practice was so many surprise and I just enjoyed the talk. Somehow I complained to the peer that I do not want to study so many system design interview, I do not want to try to memorize so many things, I like to work on the algorithm with the peer on mock interview instead.

We met and talked about one hour fifty minutes until the mock interview terminated the discussion. I could not believe that I enjoyed the discussion of the algorithm so much, I never expected that I will meet a super talent later in Saturday evening.

Time complexity

The algorithm provide by the peer is better on time complexity, since the two sum preprocessing is conducted on the iterating of the array in the same time, what ever in the hashmap should be with smaller indexes. We do not need to go through the list of the items in the key value since any one of them will work. 

It is similar to all other algorithm like merging 2 packages. 

Feedback from the peer

You just do as you do in the mock interview practice session, you should be able to do fine in any interview. That is my advice.

Being an interviewee: Array quadruplet

April 22, 2018

Introduction

It is my favorite algorithm called array quadruplet. I did talk about the analysis of the algorithm and then wrote down the algorithm without any bug and pass all test cases first time. Only thing I did is to include library using ..., I explained to the peer that I have worked on the algorithm multiple times, but one time a young lady who was preparing facebook onsite, she told me that I should simplify the code to check if dictionary contains key or not. So I only need to write three lines of code from line 57 to line 62, before I need to write if/ else and then update list in both cases.

Mock interview

Here is my C# code.

I still remembered that the first time I worked on the algorithm on mock interview platform. I had such difficult time. After I worked with over ten people on this algorithm, I followed every peer and understood how they think and analyze. So it is also very good experience to help the peer to work on the algorithm the first time. Here is the blog I wrote to give the feedback to the peer. 

4 sum algorithm

Feb. 13, 2018

Introduction

It is 8:00 PM mock interview. I spent 18 minutes to write 4 sum algorithm based on the advice from the peer, do not use extra space, using two pointer technique,  I wrote the algorithm. The total interview took us 38 minutes.

Code review

Here is C# code.

Four Sum problem

January 28, 2018

Introduction

It is busy weekend. Today I had a mock interview at 4:00 pm,  I felt that I were a student to be interviewed for an algorithm, the teacher is questioning me everything, and make sure that I understand everything I write.

Code review 

Here is the code.

Highlights of interview:

1. First the data type of function on line 44, getTwoSum, its return type dictionary's key is integer, not string;
2. Second, the array should be sorted in ascending order. I forgot to write the first round.
3. Discussion of dictionary search algorithm time efficiency.

4 sum algorithm

January 21, 2018

Introduction

It is the most popular algorithm and also my favorite one. I asked Four sum algorithm mock interview practice on the code review two months ago on stackexchange.com. This time I had to write the algorithm in mock interview at 12:00 PM mock interview, I found that it is easy to write and also I finished the analysis and coding in 30 minutes.

Code review

Here is C# code with the analysis.

A cheerful heart is good medicine

May 27, 2017

Introduction 

Proverbs 17:22, Julia's favorite verse. "A cheerful heart is good medicine, but a crushed spirit dries up the bones". Every time Julia is too busy to work on something, she starts to check whether she has the feeling of a cheerful heart, specially she likes to stay late past midnight to work on a contest algorithm. She likes to share a story of a cheerful heart, and ends her weekend with some good story.

The mock experience is related to people skills and Julia started to learn how to make most from it. She has limited resource and limited budget to try new things. She chose free mock experience, she never tried any paid mock experience, but she did feel that she has to make mock experience very good learning activities.

Always have a cheerful heart on your own or peer's mistakes, they are the best friends of algorithm problem solvers. Coding is a crafting skills, talk about mistakes, journal the transcript, and then get back to compete again.

4 Sum

People with top talent to attend mock usually are very young and just start his/ her career, and one time Julia felt that the hints were too strong in the first 5 minutes, she had to take the hint given by peer. The algorithm is 4 sum, Leetcode 18. Second time she was mocked again using similar algorithm like 4 sum, she decided to work on practice Leetcode 4 sum. Here is her practice C# code. Her second mock code is here.

Edit Distance

Julia learned so many lessons from her own mistakes. She could not figure out dynamic programming Edit Distance in her first round mock in 2017. Overall, she almost failed at least 20% - 30% in her first round.

Julia wrote a bug on spiral matrix first as an interviewee, and then she interviewed some one the spiral matrix. She observed carefully the peer's performance, she had more confident to make the code perfect later on.

Every peer get stumbles in mock experience, she reminds herself not long ago she had same experience. Julia felt so connected through mock experience.

She suddenly found out that she never met and talked to so many engineers in the world, but she did in one weekend. As a programmer, she felt a little proud of learning to review peer's code and also recommend a book "The Art of Readable Code".

Last long weekend, she managed to finish 11 mock experience. So she almost finished her second round. The fact is that second round is learning round. Test your own code, not using compiler, use your own whiteboard techniques.

Reverse string 

The fact is that she met strong peers who shared her importance to learn and write good clean code, specially recursive, DFS, and also the peer still practices. The meeting is short but she feels that the study group formed through the discussion is also very rewarding experience, she would be a nice algorithm teacher one day if she continues.

It is fun to play with a peer. One day, Julia  met a peer again and she was too busy to follow the peer's idea to solve the problem, but she knew that the peer was working hard and the idea needs to be tuned. Julia likes to gain some skills to be a professional interviewer one day, so she learned quickly to say sorry, not followed closely with the ideas in the code. Good heart leads to a new world, the peer told her that there is something new and different, she was well received with a tip.

"Every player knows how to play tennis". That is the famous tennis professional player's quote. Only those survive with strong mind set, and determination, and the hard work training, practice.

Related to tennis sports, Julia learns to treat peers equally and be supportive in mock experiences.

Julia missed how a professional mock experience will look like. She booked one mock and surprisingly she got one in less than one week.

Study and talk 

Julia wrote a blog about the study "Does mock make difference", and then she moved herself to next stage in her practice, know a professional interviewer with thousand experience, and also learn to mark herself with a mark, May 27, 2017, she got a mark which is called passing the bar - 2.5. 

Good heart leads to a new world. Julia likes to show people that she has determination to gain skills in algorithm and data structure, and is working hard on the improvement. Still exploring...

Julia understood that those contest practice with medium levels are very helpful, she prepared herself, she felt that the depth first search, recursive function call is so important to learn.

She forgets to write a base case in DFS algorithm, still she needs to the hint to go over the test case and then find out that she lets the loop forever because of that.