Leetcode discuss: 34. Find First and Last Position of Element in Sorted Array

Here is the link.

C# binary search algorithm showcase starting from August 2018

June 26, 2020

Binary search algorithm is so challenge. Since I like to train myself to perform better on mock interview, phone screen or onsite, I do have to learn how to serve others with my practice as well.

Most common errors are index-out-of-range, deadloop, and all other things like missing focus on middle and middle value. It takes so many practice for me to understand the importance of testing, even I can have ideas how to solve it, but I do have to stay humble, and also work hard to find time to practice one more time.

2020
34. Find First and Last Position of Element in Sorted Array

C# binary search algorithm practice on June 26, 2020

2019
August 22, 2019
33. Search in Rotated Sorted Array
C# various practices in 2019

A crash course in big O : Cracking the Facebook Coding Interview The Approach

Here is the link.

35:57 -

Algorithm problem : Cracking the Facebook Coding Interview The Approach

Here is the link. 

25:00 - 33:00 - 

You like to work with someone - not just solve the problem, do not care about style, optimization or other things. 

Data structures

Algorithms

Concepts

people from startup - claim to know about big O time complexity 

comfortable about basics 

Recursive

Dynamic programming 

Pattern to practice - practice those question 

Master big )

Implement DS/ Algorithms

Practice with interview questions

Code on paper/ whiteboard

Mock interviews

Push yourself 

Get comfortable about hand writing - how long it takes you to code something 

Grab a buddy to practice interview together

Cracking code interview - about hint 

System design : Cracking the Facebook Coding Interview The Approach

Here is the link. 

23:51 / 1:49:08

25:00

Cracking the Facebook Coding Interview The Approach

Do not memorize the system like Google, analyze them. 

Go to learn something like REST 

Challenging - calculate something 

How many users?

How many feeds?

How many posts in a day? 

How many ... back of envelope to calculate 

Fundamental problem solving question. 

Ask system design 

Problem solving questions 

Act like senior engineer :Cracking the Facebook Coding Interview The Approach

Here is the link.


 19:58 / 1:49:08

Drive

• Lead the process
• Be open about issues

Teamwork

• Be open to feedback
• Tweak as necessary

Act as a senior engineer, more things to talk about, tradeoffs, 

Pull them through the problem 

Technical leadership

Ask them questions - dismiss the issues I raise 

Maybe it is not the issue in the design, see how you come to go through the process

Lead the discussion 

Know less than them 

Use whiteboard 

Drive discussion - 

Be sensitive about the interviewer said

美股Facebook, Google

Here is the link.

如何获取股市里的第一桶金： https://www.youtube.com/watch?v=Hfsqy... 股市就是個大賭場，十賭九輸，那你為什麽還要炒股？要怎么做才能提高自己在股市的胜率：https://www.youtube.com/watch?v=5YXNC... 股票分析之 - Google,Facebook,Amazon,苹果,微软: https://www.youtube.com/watch?v=PV8OV... 新手投资人容易掉进的陷阱(上)： https://www.youtube.com/watch?v=lmIKh... 新手投资人容易掉进的陷阱(下)： https://www.youtube.com/watch?v=8fQl4... 如何给股票来估值？怎么判断一个股票到底是贵还是便宜？ https://www.youtube.com/watch?v=rvAoR... 公司深度分析之Google，迪士尼，阿里巴巴和拼多多： https://www.youtube.com/watch?v=jWsTZ... 特斯拉深度分析： https://www.youtube.com/watch?v=lKdjg... 苹果深度分析： https://www.youtube.com/watch?v=KkmPV... 股神巴菲特的投资理论： https://www.youtube.com/watch?v=8KxsO... 关于指数基金ETF: https://www.youtube.com/watch?v=8QKCH... 價值投資，技術分析，量化投資，組合投資，到底哪個方法更靠譜？ https://www.youtube.com/watch?v=yrpGA... 在思維模式上，富人和窮人最大的不同是什麼？ https://www.youtube.com/watch?v=CJeT-... 对冲基金是怎么赚钱的？ https://www.youtube.com/watch?v=PPlRa...

SHOW LESS

Ryan Payne on why he says investors should buy now rather than wait for a dip

Here is the link.

Ryan Payne, president of Payne Capital Management, joins "Squawk Box" to discuss how he's advising investors during the coronavirus-driven market volatility.

Ryan Payne
Rayne capital mgm

美股赚钱

Here is the link.

关注股息率是进行美股研究的一大策略；资股息率高且稳定分红的股票，是获取被动收入的一条捷径。标普500中股息率最高的能源板块，涉及石油和天然气开采、加工、存储和运输等一系列油气产业链。随着原油强劲反弹，油企的支付能力恢复，目前正是抄底能源储存运输行业的时候。股息率最高的五只美股能源股是哪些呢？请看本期节目~ 片中涉及股票代码：CVX, XOM,EPD,BP,ET

CVX  - dividend 5.97%
XOM - dividend 7.98%
EPD - 10.10%
BP -
ET - dividend 17%

美股分析赚钱

Here is the link.

book reading: Random walk ...

Here is the article. 

1. Never forget that diversity reduces adversity. Don't just buy stocks — buy stocks, bonds, and other investments classes. Within each category, diversify further. And don't just buy one stock — buy mutual funds of many stocks. (Malkiel makes his case with the stark example of a 58-year-old Enron employee who had a $2.5 million 401k — of Enron stock. When Enron went bust, the employee not only lost her job, but her retirement savings vanished completely.) Finally, the author recommends “diversification over time” — making investments at regular intervals using dollar-cost averaging.
2. Pay yourself, not the piper. Interest and fees are drags on your wealth. “Paying off credit card debt is the best investment you will ever make.” Avoid expensive mutual funds. “The only factor reliably linked to future mutual fund performance is the expense ratio charged by the fund.” In fact, the author advises that costs matter for all financial products.
3. Bow to the wisdom of the market. “No one can time the market,” Malkiel says. It's too unpredictable. Professional money managers can't beat the market, financial magazines can't beat the market — nobody can beat the market on a regular basis. The best way to earn consistent gains is to invest in broad-based index funds. It's boring, but it works.
4. Back proven winners. After Malkiel has preached the virtues of index funds, presumably converting the reader to his religion, he spends a chapter suggesting possible index funds and asset allocations.
5. Don't be your own worst enemy. Malkiel concludes by admonishing readers to stay the course, warning them against faulty thinking. He discusses the sort of money mistakes I've mentioned before: overconfidence, herd behavior, loss aversion, and the sunk-cost fallacy.

Ultimately, Malkiel's advice can be stated in a few short sentences: Eliminate debt. Establish an emergency fund. Begin making regular investments to a diversified portfolio of index funds. Be patient. But the simplicity of his message does not detract from its value. The Random Walk Guide to Investing is an excellent book because it sticks to the basics:

• It's short.
• It's written in plain English — there's no jargon.
• It's easy to understand — concepts are simplified so the average person can grasp them.
• It's filled with great advice.

This book refers often to other books to bolster its arguments, and includes quotes from financial professionals like John Bogle and Warren Buffett. Though the advice may seem elementary, it's advice that works. If you want to invest but don't know where to start, pick up The Random Walk Guide to Investing at your local library.

MORE ABOUT...Books, Investing

Stock trade: June 26 2020 7:30 AM - 9:00 AM

June 26, 2020

Introduction

It is another day in the morning I work as trader. I did make a few trades.

My transactions

I woke up around 5:00 AM, and then went back to sleep. I could not hear my alarm at 6:15 AM. I got up around 7:30 AM. 90 minutes work on stock research and my portfolio.

Stock research: 10,000 shares or $2000 profit or 3% up in major banks stock in less than 4 hours

Introduction

I like to write a short research blog about stock, investment, and my thoughts. I come out the idea to purchase 10,000 shares of HSE.TO or CVE.TO this morning when I saw SPX went up in 10 minutes with 40 points. I like to make $2000 dollars profit in less than 5 hours. Am I crazy? 

Stock market research

The market on June 26, 2020 is so crazy. The market went up and then quickly went down, and then continued to go up more than 3% - bank stock JPM, GS, WFC etc. Here is my blog. 

I just could not believe that I came out this idea to invest 10,000 shares and tried to make profit in less than four hours. June 26 2020 is the third day I got up around 6:15 and take it seriously as a business person to invest on stock market. 

Business is out-of-order but stock market is still under control. Should I discipline myself as an investor, I just got up early and started to watch market less than a week. 

Will I lose everything in stock market?

June 26, 2020

Introduction

I like to write a short research blog about stock, investment, and my thoughts. I come out the idea to purchase 10,000 shares of HSE.TO or CVE.TO this morning when I saw SPX went up in 10 minutes with 40 points. I like to make $2000 dollars profit in less than 5 hours. Am I crazy?

Stock market research

The market on June 26, 2020 is so crazy. The market went up and then quickly went down, and then continued to go up more than 3% - bank stock JPM, GS, WFC etc. Here is my blog.

I just could not believe that I came out this idea to invest 10,000 shares and tried to make profit in less than four hours. I do see the opportunity to make $2500 profit in less than four hours using my TFSA questrade.com account.

Business is out-of-order but stock market is still under control. Should I discipline myself as an investor, I just got up early and started to watch market less than a week.

Leetcode post: Requesting guidance from those who solved 1000+ Leets so far!

June 25, 2020

Here is the link. 

Thank you for good question.

I wish that I can solve 1000 algorithms one day. I am so busy to go through learning in personal finance, stock investment etc. So I took a break almost from January to June 2020.

I only solved 468 algorithms and I did spend over six years. Over years I learn my most favorite teaching method - Harvard business school case study method. So I share every practice I work on starting from 2019 August.

I choose to work on easy level algorithms first since I got a private coach for 1000 minutes, he gave me the advice. I had tough time to master tree algorithms, so I asked the lowest common ancestor tree algorithm over two months back in 2019. I did find my issues, since I document every practice, ugly ones showed up and I learned backtracking starting from my bad practice on the algorithm.

I am preparing for Facebook phone screen in July 2020. Now I am rushing to take Leetcode mock interview as many as I can next two weeks. I start to solve new algorithms through mock interviews. Also I learn the importance to solve those mock interview algorithms. I have to maintain my performance by solving in limit time, beat 90% others if I can. Right now, I still take too long to work on an easy level algorithm, problem to trouble shoot bugs in my code. I need more practice regularly.

I will try to solve another 100 algorithms in two weeks. Another 500 algorithms will take me a long time. But I do think that most of important is to teach and share, and work together with top talents in the world. I interview on interviewing dot io as interviewer. Learning from top talent engineers is much better way to push myself, stay connected to the world as a software engineer.

10 common mistakes in investing on US stock market

1. June 25, 2020

Introduction

I learn so many lessons as an investor. I like to write down what I have learned and then hopefully I can become a better investor.

10 common mistakes

I have to learn how the company works as a business. Right now, there are so many distressed companies and so many layoffs, and so many people are struggling to pay mortgage and other things.

I like to see if I can become a better investor by writing down my mistakes.

1. Be careful when SPX is high like 3200, do not hold stocks purchased on high SPX index; 
2. Example for item 1, I lost $3000 US dollar in market value in less than two business days after I made purchase on June 5, 2020. I did not know the market was so volatile, and there are so many dangers out there in the market;
3. Understand the business and my own emotions as an investor. Try to read more articles about business and problems ahead related to Coronavirus; 
4. Example for item3, I start to learn US business. What are those essential ones for me to understand first; 
5. ....

Leetcode discuss: 3. Longest Substring Without Repeating Characters

Here is the link. 

C# warmup practice in June 25 2020

June 25, 2020

Introduction

The problem is to find longest unique substring. It is a classical algorithm for sliding window technique. I wrote one using two nested loops, so I like to write second one using one loop only.

I also like to write a solution based on simple structure of code, only use one loop - while loop. How to write quality code involving good design - avoid index-out-of-range error, simple structure of code as well.

Case study
"aab"
Sliding window can be marked using two variables, one is left, one is index; both start from 0. Each char will be checked if it is duplicated or not. If it is, then the char will be removed from hash set found, and also left pointer increments one. Otherwise, the char will be added to found hashset, and then update max - size of sliding window containing unique characters, move to next iteration.

I practice a solution using two loops. Here is the link. So I like to write a solution to use only one loop instead.

Time complexity
O(N), N is the length of string.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _3_longest_substring___review
{
    class Program
    {
        static void Main(string[] args)
        {
        }

        /// <summary>
        /// code review on June 25, 2020
        /// "a"
        /// "aa"
        /// "abc"
        /// </summary>
        /// <param name="s"></param>
        /// <returns></returns>
        public int LengthOfLongestSubstring(string s)
        {            
            if (s == null || s.Length == 0)
            {
                return 0;
            }

            int length = s.Length;

            var found = new HashSet<int>();

            int max = 0;                     

            int left = 0;
            int index = 0; 

            while(index < length && left <= index)  // caught by debugger - add left <= index
            {
                var current = s[index];   
                var duplicate = found.Contains(current);  
                var leftChar = s[left];  

                // duplicate char to remove
                if (duplicate)
                {
                    found.Remove(leftChar);  
                    left++;                   
                    continue; 
                }

                found.Add(current);                                  
                
                max = Math.Max(max, index - left + 1);  
                index++;                                                    
            }

            return max;
        }       
    }
}

Leetcode discuss: 1089. Duplicate Zeros

Here is the link.

C# mock interview 60 minutes practice on June 25 2020

June 25, 2020

Introduction

It is my first algorithm in mock interview on Leetcode.com. It took me almost 60 minutes to write code and made it work. I like to work on a case study, and then write down some notes for me to work on.

I have to prepare Facebook July 2020 phone screen. I like to work on 100 algorithms on Leetcode through Leetcode mock interview phone screen practice. So far, I only finished 6 algorithms.

Case study
Problem statement:
duplicate 0 in the array, and try to fit in the array in place from end of the array.
For example:
[1, 0] -> [1, 0]
[1, 0, 1] ->[1, 0, 0]
[1, 0, 0, 1] -> [1, 0, 0, 0]

The simple idea is to calculate how many numbers in the array can fit in the same array from left to right. Edge case is last number, it may be a zero, but only one position left for that zero.

I chose to take risk of index-out-of-range, I tried to cut number of variables to minimum, so the code can be clean and easy to read and test.

I added the comment to mark the bugs I made in my writing, and then I caught the issue through visual studio debugger. Every bug will take me a few minutes to fix, and I should think about better design in terms of definition of variables at the very beginning.

Mock interview performance - only beat 30%
I have to challenge myself to think about how to define variables more clearly defined.

//[1,0]
    public void DuplicateZeros(int[] numbers) {
          if (numbers == null || numbers.Length == 0)
                return;

            var length = numbers.Length; //2     - bug 1
            var next = 0;
            var last = 0;

            for (int i = 0; i < length && next < length; i++)  // caught by debugger - length mixed with length + 1, what is good design? < or <=, think about more about common ways 
            {
                var current = numbers[i];//0

                // keep last i
                last = i; // 0

                if (current == 0)// true
                {
                    next += 2;    // 3                            
                    continue;
                }

                next += 1; // 1                       
            }

            int end = next - 1;  // 3       should be next - 1, why the design needs -1 here? Not good design. 

            for (int i = last; i >= 0; i--) // last = 2
            {
                var current = numbers[i]; // 0
                var isZero = current == 0;

                if (!isZero)
                {
                    numbers[end--] = numbers[i];
                    continue;
                }

                if (end > length - 1)
                {
                    numbers[length - 1] = 0;
                    end -= 2;   // caught by debugger - forget to take 2 off
                }
                else
                {
                    numbers[end--] = 0;
                    numbers[end--] = 0;
                }
            }
  }

Leetcode discuss: 1007. Minimum Domino Rotations For Equal Row

Here is the link.

C# mock interview practice on June 25, 2020

June 25, 202
Introduction
It took me less than 22 minute to finish code and also fixed the bug in my design as well. I like to write down my analysis and explain to myself how to solve the problem

Case study
Go over the example, how to find the target number, and which array should be dorminant one to get minimum rotations.
[3, 5, 1, 2, 3]
[3, 6, 3, 3, 4]
By my observation, I should find number 3, and also array B has 3 number 3.
I argue that the array should have a count of number from 1 to 6 at least half of (length + 1).

But after the code submission, I failed one with more duplicate same number in another array. My argument is not correct. I have to consider all possibles and then get minimum one from all options.

Mock interview performance - beat 30%
I have to work on the first easy level algorithm, so my performance can be better to beat more people.

public class Solution {
    public int MinDominoRotations(int[] A, int[] B) {
        if(A == null || B == null || A.Length != B.Length || A.Length == 0)
            return -1; 
        
        var length = A.Length; 
        
        var countA = new int[7];
        var countB = new int[7];
        for(int i = 0; i < length; i++)
        {
            countA[A[i]]++;
            countB[B[i]]++;
        }
        
        var number = -1; 
        var foundA = false;
        var foundB = false;
        
        var candidates = new List<Tuple<char, int>>(); 
        
        for(int i = 1; i < 7; i++)
        {
            if(countA[i] >= (length + 1)/ 2)
               { 
                
                 foundA = true; 
                 number = i;
                 candidates.Add(new Tuple<char, int>('A', i));
                 break;
               }
        }
        
        for(int i = 1; i < 7; i++)
        {
              if(countB[i] >= (length + 1)/ 2)
               { 
                 foundB = true; 
                   number = i; 
                   candidates.Add(new Tuple<char, int>('B', i));
                   break;
               }                 
        }
        
        int min = length + 1; 
        foreach(var option in candidates)
        {
            var target = option.Item2;
            var result = -1; 
            if(option.Item1 == 'A')
            {                
                result =  countMinimum(A, B, target);                 
                
            }
            else
            {                
                result =  countMinimum(B, A, target);                             
            }
            
            if(result != -1)
                {
                    min = Math.Min(min, result); 
                }
        }
        
        return min == (length + 1)? -1 : min; 
    }
                 
    private int countMinimum(int[] A, int[] B, int number)
    {
        int minimumCount = 0; 
        
        for(int i = 0; i < A.Length; i++)                 
        {
            var current = A[i];
            var isTarget = current == number;
            if(!isTarget)    
            {
                if(B[i] == number)
                {
                    minimumCount++; 
                }
                else
                {
                    return -1; 
                }
            }
        }
        
        return minimumCount; 
    }
}