Draw a circle algorithm

August 18, 2015

Interesting problem – draw a circle,

blogs to read:

1. http://petercai.com/the-microsoft-sde-interview/

2. http://www.startuplessonslearned.com/2008/11/abcdefs-of-conducting-technical.html

3. https://en.wikipedia.org/wiki/Midpoint_circle_algorithm

C# code I wrote in Dec. 2012 is here. 

Follow up 

January 23, 2018

I traced my outlook email and then I found out that it is one of my phone screen algorithm I got in 2012. I supposed to write in 20 - 30 minutes, and at most 40 - 50 minutes.  

"More detail about the draw circle program, in first 10 minutes, I came out a mediocre solution, an then I tried to catch up while coding to put more ideas in, so I changed the original idea to set a target, and then made this 1000 tries to reach the target; the algorithm is like an undetermined optimal algorithm, with a lot of mistakes, losing the focus sometimes. I should have clarified the requirements with you before I started yesterday and work in the right direction. "

It is such a great feeling to read what I wrote in 2012. It is more than 6 years ago. At that time, I was too shy and I did not have habit to write daily. And I still remembered that I was so excited to have a phone screen, at that time, as a software developer, I was too isolated and my personality was kind of introvert. I was afraid to write down what I think at that time.

C# code I wrote in Dec. 2012 is here. Read the code I wrote more than 6 years ago. How to define the feeling? It is like meeting an old friend, sweet and sour. But this time the sour is mild level, code smells make the sour feeling. 

Code review and then C# code is written, the link is here. 

Leetcode Question No 70: climbing stairs

July 28, 2015

Problem statement:

You are climbing a stair case. It takes n steps to reach to the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

The problem is most popular question in the algorithm, so I do like to spend time to find out all sorts of solution, and get myself comfortable to all kinds of ideas, and figure out which one is best, and all concerns we can have in the discussion of climbing stairs:

1. Recursion solution vs. DP problem solution (Dynamic Programming solution)

2. Time complexity solution: O(2^n) vs O(n) solution

3. The space O(N) vs O(1), in other words: array of N or 2 variable, and another tmp variable

4. The base case discussion: f(0) = 1 or f(0) =1, math question?

5. Math formula - closed form solution vs DP problem solution
6. Use Memoization DP vs. no memoization DP
7. Programming skills, how to make code easy to follow, more readable, more abstract. 

The investment of time on the problem is well done. Go over 16 implementation one by one using C# programming language. 

C# code:

https://github.com/jianminchen/climbingStairs/blob/master/climbingStairs.cs

其实, 我觉得题目越容易, 越值得投入时间去学习; 看看大家有没有不同的理解, 打开思路; 如果自己没有训练过这道题, 可能会紧张; 即使训练过, 但是, 有的想法, 可能自己从来没有思考过, 一时还不能判断好坏, 但是, 多看网上的博客, 向每一个人取取经. 谦虚, 才能有提高.

我编网站后台, C#程序自己写; 自己训练的题目太少; 这次选择用Leetcode来提高C#编程, 又可以提高算法和数据结构的知识, 网站后台靠平时训练.  

January 3, 2016

Review the leetcode question 70, climbing stairs. 

Read the blog:

http://blog.csdn.net/kenden23/article/details/17377869
http://yucoding.blogspot.ca/2012/12/leetcode-question-15-climbing-stairs.html

http://www.cnblogs.com/springfor/p/3886576.html

http://www.cnblogs.com/springfor/p/3886576.html

http://siddontang.gitbooks.io/leetcode-solution/content/dynamic_programming/climbing_stairs.html

https://github.com/zwxxx/LeetCode/blob/master/Climbing_Stairs.cpp

Leetcode: Count Primes

On June 22, 2015

Problem statement:

Count the number of prime numbers less than a non-negative number, n

Hint: The number n could be in the order of 100,000 to 5,000,000.

Read the article to talk about how to improve skills as a programmer, one comment I like most:

http://blog.csdn.net/gsky1986/article/details/46556933

"那你应该可以一眼就看出满世界的博客的算法文章中的纰漏和层次，那你还是有点功力了", 我现在还没有功底, 专心在Leetcode, 专心用C# 语言; 提高提高自己写C#代码水平.

Share the C# code in github:

https://github.com/jianminchen/count-primes/blob/master/Program.cs

Leetcode question 66: plus one

June 22, 2015

Given a number represented as an array of digits, plus one to the number.

Leetcode: plus one, 喜欢这道题, 看看有哪些解法; 一个个试过来 (6种方法).
Read the web blogs, and then, try different solutions (Six implementations).

practice using C#, the source code on github:

https://github.com/jianminchen/math-plus-one/

https://github.com/jianminchen/Leetcode_C-/blob/master/66PlusOne.cs

Try different solutions through blogs, and then, catch up something interesting; basic programming styles, for loop, while loop, and different ways to check carry, using %, /, ==10, ==9; one problem can be interpreted with different solutions. Fun time to play with source code, and get familiar with basic C# stuff, array, initialization.

Leetcode: Power(x,n)

June 10, 2015

This question is most popular question in terms of my personal experience.

http://fisherlei.blogspot.ca/2012/12/leetcode-powx-n.html

http://fisherlei.blogspot.ca/2012/12/leetcode-powx-n.html

http://yucoding.blogspot.ca/2013/03/leetcode-question-74-powxn.html

best blog I have seen:

power(x,n)

http://rleetcode.blogspot.ca/2014/02/powx-n-java.html

http://www.lilongdream.com/

http://www.lilongdream.com/2014/04/10/94.html

http://www.shuatiblog.com/blog/categories/leetcode/

check this blog and ensure that it makes good sense to read it.

http://www.shuatiblog.com/blog/2014/05/28/Best-Time-to-Buy-and-Sell-Stock-III/

http://codingtnnd.blogspot.ca/2014/09/powx-n-leetcode.html

Share C# code: 

https://github.com/jianminchen/powerOfN/blob/master/Program.cs