Code Review stackexchange.com ranking page - a short research

January 10, 2016

Introduction
Julia found out that she had 6% performance tag next to her name, and then she felt so good after she worked on them last 48 days. So, she decided to study the ranking page, spent over one hour to find something to work on.

Study the ranking statistics:

Actionable Items: 

Julia will spend some time to look into 5,000+, less than 200 people, check 10 people a time.

Julia drills down what she did from January 5 - January 10, 2017

134 reputation - Julia gain 34 reputation by posting two code reviews - one is called "Simple Function", another one is called "Find kth largest element in the union of two sorted array". 

Research

Most of important, she found out the best algorithm teachers she can find, and learn from the answers.

1. score over 1122 points on JavaScript - link is here.
2. score 880 algorithm points - link is here.
3. score over algorithm 459 points - link is here.
4. score algorithm 200 points - link is palacsint.
4. Go through algorithm score ranking - link is here.

Study those top algorithm answerers:

Study those top algorithm askers:

Top JavaScript Askers - click here.
Julia's favorite 66 code review by views - click here.

20 algorithm questions - click here.
One algorithm can turn into a fun day. And also see chat room works.

Reversing k size sequence in a linked list. Code review makes perfect.

Longest palindrome string - best review - no raw loop.

Pluralsight: Encapsulation and SOLID

January 10, 2017

Introduction
Julia did some research on stackexchange.com ranking page over one hour, then she found one of talents also teaches on pluralsight.com. Last 2 - 3 months, Julia did not have taken any course. She likes to plan to study the course.

Unbelievable, Julia saw something making her smile, the first 10 days of new year 2017.

Remember the joy, and also first few algorithms she asked, people rushed to help Julia out, and help her write, think and reasoning,  she learned to write her own work, first time she earned the privilege to give out up-vote, Julia found a community to get connected. Have some visual thing to help the celebration of 48 days journey.

Plan

Study the course: Encapsulation and SOLID by Mark Seemann

Stackexchange.com code review - bonus reputation

January 8, 2016

Julia has a good news to share, she got bonus reputation 100 for code review on stackexchange.com.

Here is the snapshot of the message she got for 8 sites. She got 800 bonus reputation.

Code Review: Sherlock and Anagrams

January 8, 2016

Introduction

Julia worked on the code review by one user third time, she plans to review all submissions from the same user. 

Workout

First algorithm review -

Sherlock and Anagrams

Julia worked on the algorithm, here are her previous blogs about the algorithm:

Practice I

Practice II

Practice III

Practice IV

Practice V

Practice VI: Warmup after 3 months

Spent some time to go over code:

Read editorial notes, and also have some practice using C# on January 8, 2016.

Another practice using C#.

January 22, 2017 

Another practice, C# code is here.
study code review done by mdfst13, review is here.

Tennis coaches and their sharing of teaching

January 8, 2016

Introduction

Julia starts to show strong interest on tennis coaches study after she wrote her first post about tennis coach Rob Steckley on Dec. 26, 2016. Specially, when she experienced the nervousness to prepare a 75 minutes coding assignment and rushed to find help, she knew that sometimes she let nervousness take over, domino effect may happen, because she is still a weak player without strong disciplines and a lot of trials and errors. Algorithm player and tennis sports are two sports Julia trains herself hard.

Julia knew that she had weakness on her English skills, she has to push herself write down something every day; and also, recently, she likes to clean out the blog page content, for example, do not show link url instead of showing some interesting context, pay attention to small detail, specially after she starts to learn aesthetics in design,  read the book the art of readable code (Part I. Surface-Level Improvements - chapter 4: Aesthetics); she learned a few things from stackexchange.com code review, when her posts were edited by various people.

Patrick Mouratoglou and Darren Cahill US open interview, Julia chose to study the interview again, and this time, she likes to document the coach's talk, how coaches help tennis player express the anger in the match, and how to relate to her own experience in sports and also in competition of software programming contests.

Workout 

Julia has to pay attention to her English skills, and then work on small task once a while. Take down notes from the coaches, and continue to do some research.

Will spend one hour to take notes first. Will come back very soon.

1:58pm
Darren Cahill:
Former coach of Agassi & Hweitt
1988 US Open Semifinals
Current coach of Simona Halep

Simona threw the racket - how did coach guide her on releasing her anger properly?
Consistency, consistency in the training. Consistency in the game plan, then be able to evolve as a tennis player as well, not stick to one thing at all; If something is not working, you have to find other ways to win in tennis matches. At the beginning to work with Simona, if something is not working, then bring out domino effect, a lot of loss of points afterwards, affect the game. She is doing much better right now, isolate that thing, move to something working.

In perfect world, no to Simona's action to throw racket on the ground. You want the player to keep those emotions inside. But she is Romania, she has a fire in the belly. They like to express themselves, especially Simona. And my biggest issues are if you do get angry, that is fine. But do not filter through next 2, 3 points, and let games get away from you. But we just need to get her a few rackets.

Code review by User (III)

January 8, 2016

Introduction
Julia woke up in the middle of the sleep, and then she checked her two posts on code review, she was amazed that in her 3 hours sleep she got 3 up-votes. Actually she went bed around 2:00am, she posted 2 algorithms for code review. What a bad unhealthy life style - let internet ruin the good sleep.

She knows that she has to learn how to play a good game about reputations, and do not let reputation take over her strong analytical mind she is trying to build up. At 9:48am the morning, her reputation is up to 189, 20 more reputation compared to 2:00am, January 8, 2017 when she went to sleep.

One of algorithms is about simple function. Link is here. She got 2 up-votes, each brings 5 reputation.
Another one is about "Find kth largest element in the union of two sorted array". Link is here. She also got 2 up-votes.

She taught herself to be very patient in Saturday, spent over 4 hours to work on Hackerearth simple function again, and learn whatever she has to do. She got feedback from her post - the code is hard to follow, where code is rewritten from her study other player's C++ code. One algorithm a time (This algorithm Julia worked on more than 2 * 10 hours). So, she likes to avoid complicated code, and work with high reputation talent (For me that solution is hard for follow – Paparazzi Jan 2 at 15:12 about Julia's post) better, she said goodbye to her old post and all her concerns to work on the follow-up post.

So, most of important is to have some sportsmanship, check other people's post, and give out an up-vote as well. Think about others, give out some encouragement as well. The small sportsmanship leads her to do a study on a post by this user.

Workout

Julia experienced the excitement from reputation going up 20 from 169 to 189, after she worked on algorithm more than 8 hours in Saturday, January 7, 2016. Now she is imaging that how much work she has to complete in order to make this reputation go up to the user - CodeYogi 1683, top 8% overall. 

100 algorithm, have some time to study peers. 

First algorithm review -

Sherlock and Anagrams

Julia worked on the algorithm, here are her previous blogs about the algorithm:

Practice I

Practice II

Practice III

Practice IV

Practice V

Practice VI: Warmup after 3 months

Facebook hackercup qualification round - Fighting the Zombie

January 7, 2017

Julia likes to get some experience on this - she likes to have some adventure for 2017.

• Online Qualification Round: January 6, 2017, 4pm PST - January 9, 2017, 4pm PST (72 hours)

Here is the link to get some experience. 

The progress pie - the third algorithm. 

Plan to spend as many hours as I can this weekend. Enjoy the qualification round.  

Facebook hackercup qualification round - lazy loading

January 7, 2017

Julia likes to get some experience on this - she likes to have some adventure for 2017.

• Online Qualification Round: January 6, 2017, 4pm PST - January 9, 2017, 4pm PST (72 hours)

Here is the link to get some experience. 

The progress pie - the second algorithm. 

Plan to spend as many hours as I can this weekend. Enjoy the qualification round.  

Exercise and the brain

January 6, 2017

Watch the video by Wendy Suzuki - a professor of New York university.

http://www.wendysuzuki.com/

Facebook Hacker Cup 2017 - The progress pie

January 6, 2017

Julia likes to get some experience on this - she likes to have some adventure for 2017.

• Online Qualification Round: January 6, 2017, 4pm PST - January 9, 2017, 4pm PST (72 hours)

Here is the link to get some experience. 

The progress pie - the first algorithm. 

Plan to spend as many hours as I can this weekend. Enjoy the qualification round. 

Trust your struggle

January 6, 2016

Trust your struggle - Zain Asher - CNN Anchor, a very nice and well-prepared talk around 14 minutes.

Zain Asher Bio is here.

3 beliefs:

1. Hard work is not all. Trust your struggle. The hardship you go through will be your own benefit.

2. Not believe competing what you want, but creating what you want. Do not need to take anything from others.

Abraham Lincoln: The best way to predict your future is to create it. 

Instead of competing, compare yourself again and again, actually bring out fear, insecurity and actually hold you back. 

3. The more you give, the more you receive.

Interview Kat Cole, is something different: The more you give, the more you receive.

You have to network, have a brand, and study your competition.

Loosely related to hard work, success comes when opportunity meets preparation.

Her brother is an actor - master to prepare early, very well.

Trust one day, the opportunity will come. Not prepare for interview.

Teach herself about stock, finance, a few years. After she prepared for financial study for a few years, she had chance of 2 weeks to prepare for the screen test and financial test, for a position of finance reporter in CNN.

What one skill = an awesome life?

January 6, 2017

What one skill = an awesome life? | Dr. Shimi Kang | TEDxKelowna

8 Do not - Relax and Be Yourself

January 5, 2016

Be yourself and relax in 2017. It will be a great year for hard working people, Julia, you are one of them.

A - Do not act like you know everything.    (I am still learning, do one thing a time.)
B - Do not be a hero.                      (I make mistakes, and then know how to calculate the risk better)
B - Do not be overly format.  (Specially, do not purchase too many clothes.)
O - Do not over-prepare.        (Treat yourself as a human being. Stay in the moment. )
P  - Do not panic if a problem stumps you. (Nobody is perfect. Even champions will fail over and over again.)
S - Do not second-guess yourself.   (Practice makes perfect. Do one thing a time)
S - Do not stress if you are not a 10X coder. (Julia, you fail so many times in programming contests, then you learn the difficulty of problem solving.)


Review the interview cheat sheet blog's notes, write down most favorite ones:

1. Don't be overly format. "Don't act like somebody you're not - it's really a come-as-you-are environment."
2. Don't second-guess yourself. "You have to have confidence in your ability to make connections, because executives are going to challenging your recommendations. You'll be expected to back them up."
3. Don't act like you know everything.
4. Don't stress if you're not a 10X coder.
5. "The interview isn't grading you on your improv skills, but whether you steer difficult conversations forward without falling for distraction."
6. Don't be a hero. "Be able to articulate your specific contributions instead of doing everything yourself."
7. Don't over-prepare. "Planning everything you're going to say and do in the case study portion of the interview makes for a stale presentation and misses the mark. The point of the case is to see how you approach problems in real time."
8. Don't panic if a problem stumps you. "We're really trying to assess your thought process, so if you get stuck or make a mistake, don't stress out - nobody is perfect."

Be an inspiration 🙌

A photo posted by Caroline Wozniacki (@carowozniacki) on May 3, 2015 at 9:29am PDT

The kth largest element from two sorted arrays

January 5, 2017

Introduction
Spent over 2 hours to study Leetcode 4 and Leetcode 215: the medium of two sorted array, and then Leetcode 215: the kth largest element from the array, and then, Julia spent over one hour to work on the code for the algorithm: the kth largest element from two sorted array.

Workout

Here is the C# practice: binary search, time complexity: not O(lg n + lg m), smaller one: O(lg(n+m)), n, m are the length of two sorted arrays.

Julia likes to work on the test case a little more time, 20 - 30 minutes, and then post the algorithm on stackexchange.com for a code review.

Read the article again, learn more about the analysis.

January 9, 2017
The most important feedback about the code - code review:
Just so you know, your solution appears to be O(logk∗(n+m))$O(\log k\ast (n+m))$. The reason is that ArraySplice() makes a copy of the array, which takes either O(n)$O(n)$ or O(m)$O(m)$ time. If you would just avoid doing the copy and instead pass a starting index for each array to your function, you would be down to O(logk)$O(\log k)$ time. – JS1

Actionable Items:

1. Read a few articles about the algorithm, list here:

2. Write a new version of algorithm to solve all issues, post it on code review. Learn by doing.

3. C# practice with the correction of time complexity issue - array splice. Code is here.

Code review by user (II)

January 5, 2016

Review all 65 question asked by one user.

1. Buy once and sell once for maximum profit

solutions for 3 algorithms: once, twice, or at most twice

2. Check if two rectangles overlap

Leetcode 223 rectangle area - solution with a graph

3. Find median of two sorted arrays

Review the blog written in 2015, and one in 2016. 

code review:

Median of two sorted equal sized arrays on combination

Leetcode 215 Julia's C# practice

Code Review: Social network broadcast message algorithm

January 5, 2017

Read two code reviews:

1. Social network broadcast message algorithm

2.   Social network broadcast message algorithm (part 2)

Code Review: Minimum Spanning Tree

January 5, 2017

Review minimum spanning tree

Minimum Spanning Tree using Prim's algorithm

Look into those reviews: very good advice about global variable. 

Leetcode 333: Largest BST subtree

January 4, 2016

Start from here, and then study the code written by the expert.

Top-down O(n!) vs bottom-up O(n), very good discussion. Here is the link.

Leetcode 210: Course Schedule (II)

January 4, 2016

Review Leetcode 210.

Study the solution here first.

Review previous practice here.

Just warm up graph algorithm in 30 minutes:
Study graph on code review website on stackexchange.com.

1. First review of BFS, DFS - Excellent review link is here. 
2. Implementation of Graph - Good review link is here. 

3. Implementation of Dijkstra's algorithm

[interview-questions] graph keyword search: 35 posts sorted by vote 

1. Find if a word with wildcard exists in dictionary [closed]

     Good lecture about test driven development

Algorithm study

January 2, 2017

Plan to spend some time to go over the algorithms one by one.

Go over those algorithm first:
K Closest Points
Longest Palindrome
Rectangle Overlap
Window Sum

Copy List with Random Pointer
Five Scores
Maximum Subtree
Minimum Spanning Tree
Order Dependency

Coding Questions:

A

Arithmetic Sequence

B

BST Minimum Path Sum

C

Copy List with Random Pointer

D

Day Change (Cell Growth)

F

Five Scores I
Five Scores II

Four Integer

Find Optimal Weights (Close Two Sum)

G

GCD Greatest Common Divisor

Gray Code

I

Insert Into Cycle Linked List

K

K Closest Points

L

Loop in Linked List
LRU Cache Count Miss

M

Maximum Minimum Path

Maze
Minimum Spanning Tree I
Minimum Spanning Tree II

Merge Two Sorted Lists

Maximum Subtree of Average I
Maximum Subtree of Average II

O

Order Dependency I
Order Dependency II

R

Remove Vowel

Round Robin
Rotate Matrix

Rotate String
Reverse Second Half of Linked List

Rectangle Overlap

S

Same Tree
Subtree Check

Shortest Job First

Sliding Window Maximum(Minimum)

Search a 2D matrix

Search a 2D Matrix II

T

Two Sum Count

Tree Amplitude

V

Valid parentheses

W

Window Sum

Blog reading:
https://segmentfault.com/t/amazon/blogs

Perfect interview

Leetcode 240: Search a 2D Matrix

January 2, 2017

Problem statement

Introduction

Study the code written in two solutions, first one is time complexity O(log(m*n)) using binary search and second one using binary search is O(logm + logn).

Workout

Study C++ code first. 

Matrix Rotation Study

January 2, 2017

Introduction
Julia learns the hard way. This past 2016, Julia worked on matrix rotation practice (No.1) again in April, 2016, she failed to deliver the ideal result in one hour setting. And then, she came back to work on matrix rotation so many times. Hackonacci Matrix rotation - algorithm on HackerRank week code 27, Julia spent more than 4 hours to review all submissions, she did learn the hard way - in the contest she spent more than 3 hours to write code, but scored less than 10% in Dec. 2016.

Now, she came cross this study about using transpose and flip code again, now she was smart and mature enough to take it and be the master of matrix rotation time saver.


Workout

Use transpose and flip operations


Another code of transpose and flip with a flag to separate clockwise from anti-clockwise.

Julia's C# practice.

Hackerrank - Ad Infinitum 17

January 1, 2016

Julia likes to get more experience to play contest, she is very busy on January 1, but she likes to spend 2 - 3 hours to work on the contest, and get some experience.

Focus on reading, be able to understand the algorithm, improve her English reading, solve problems quickly.

Will come back very soon.

2017 New Year's day - Code Review: Connected Cell in a Grid

January 1, 2017

Ask questions on code review.

Connected Cell in a Grid - Warm up with Five Practices

Spent 2+ hour to put together C# code to post a review request.

Ask ideas how to add some debug code to track quickly/ efficiently the design:

1. Queue - in/ out as designed
2. Connected Region - counting of cells is correct
3. Check how many regions are counted
4. Basically, talking about tips to help development of code, not affect the presentation of code.

Here is the code review feedback:
boundary check and user input handling

Hackerearth "January Easy '17 contest" Simple Function

January 1, 2017

Plan to attend 8:00 - 11:00am hackerearth.com

January Easy '17 contest

Work on the algorithm:

January Clash '2017


- One of 6 algorithms: Simple Function

In contest performance, C# solution, pass test case 1, but timeout all other cases. (9:00am - 11:00am)

C# solution, passed 5 test cases, fail last one. (after the contest, 2+ hours)

Study code C++

Write C# code using the above solution. (Time spent: 4 + hours, completed at 6:37pm)

Code Review Link is here. Julia spent more than one hour on January 3, 2016 to add her calculation of cache size reduction from 2MB to 80KB based on the comment from Paparazzi


January 7, 2016
Continue to do some research on C# Dictionary comparison to self-defined hash function to do pre-processing.

Using Dictionary<string, int>

C# with Dictionary code:

Test result from hackerearth.com:

The time complexity analysis:
function CalculateSumOfEvenNumbers(), inside two loops, function GetLastDigit(...)
is called; inside GetLastDigit() function, there is a HashSet to prevent
duplicate calculation, and then, GetLastDigit() is called; inside GetLastDigit(),
two calls of the function GetDigits(). Actually, we only care about two integer
number, biggest same digit, and we do not care about how many digit inside
each integer. And this approach goes over each digit in the integer.



Self-defined hash function

Comparison to the self-defined hash function - code is here:
The performance:

Time analysis:

For each query, process two baskets of integers,  two separate loops, O(N1 + N2), detail see function ProcessInput(...); For each number, call Hash function to process, any number is at most 4 digits, each digit, only do one calculation to determine the digit from 1 to 9. Just a minus arithmetic calculation. Detail see the function Hash(char[] cache, int nthNumber, int serialNo)

To calculate the even number count, call function CheckNumberIsEven(...) N1 * N2 times, each function call, only need to look up at most 10 times, find a match then break the loop.

So, overall, time complexity is O(N1+N2) + O( N1*N2), is around O(10^6) calculation of CheckNumberIsEven function which includes a few of arithmetic calculations; the self-defined hash function is almost less than 1 percent of time to compare calculation the even number count.

Digits Internal Class

Another C# version, no Dictionary, just use int[10] to store an integer, with digits. No string manipulation to get the substring. Pass all test cases. Code is here.

Performance:

HashedInteger Class

Digits class name is not very meaningful, so HashedInteger class name is chosen to replace Digits.
And also Save API is not clear, add Convert, ConvertAll APIs instead.

The code is here.

Code Review - Find biggest basin

Dec. 31, 2016

Find biggest basin

Julia's favorite review: 

http://codereview.stackexchange.com/a/49477/123986

Julia, write a C# practice as well.

BFS/ DFS algorithms' Review

Julia, please review BFS/ DFS algorithms practiced this year.

Search blog using keyword: BFS

1. Connected Cell in a Grid - Warm up with Five Practices

Use Queue/ Stack/ Recursive function, get familiar with all five algorithms.

2. Leetcode 317: Shortest distance from all buildings