Island count

June 30, 2018

Introduction

It is my 4:00 PM mock interview. I had to work on the algorithm called Island count. After I explained the algorithm to the peer, peer asked me if I like to continue to write the code for the solution, or I like to discuss with the extended algorithm. I chose to discuss the extended algorithm.

Extended algorithms 

I was asked to work on the extended algorithm. Here is the transcript for our discussion. I need to write code for those two extended algorithms.

Follow up No. 1


Follow up No. 2

Feedback

It is also a good idea to work on the feedback from the peer.

My feedback to the peer

Here is my feedback.

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.

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.

Breath first search algorithm

Nov. 24, 2017

Need to code review two practice on breath first search.

First one is on Nov. 16, C# code is here.
Second one is on Nov. 24, C# code is here.

Code review 

Copy the idea from code review here.

C# code is here.

Leetcode 102: Binary tree level order traversal

July 23, 2015

Problem statement:

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3
   / \
  9  20
    /  \
   15   7

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

写代码发现很多问题. 程序要多写, 多练. 背算法可能也是一个途径. 从C++代码, 转化成C#, 犯了几个错. 一下学习到很多C#知识, 感觉不错! 练习6种方法. 

1. Solution 1: (push extra null node in the queue to divide level)

Read the blog:

https://github.com/xiaoxq/leetcode-cpp/blob/master/src/BinaryTreeLevelOrderTraversal.cpp

convert it to C# code:

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

C# code passing leetcode online judge:

https://github.com/jianminchen/BTreeLevelOrderTraversal/blob/master/BTreeLevelOrderTraversal2.cs

Solution 2: (using 3 variables to help queue to do BFS algorithm)

blog:

http://fisherlei.blogspot.ca/2013/01/leetcode-binary-tree-level-order.html

C# code:

https://github.com/jianminchen/BTreeLevelOrderTraversal/blob/master/BTreeLevelOrderTraversal3.cs

Solution 3: DFS algorithm:

blog:

http://fisherlei.blogspot.ca/2013/01/leetcode-binary-tree-level-order.html

C# code:

https://github.com/jianminchen/BTreeLevelOrderTraversal/blob/master/BTreeLevelOrderTraversal4.cs

Solution 4: using two containers for current level, next level 

blog:

http://bangbingsyb.blogspot.ca/2014/11/leetcode-binary-tree-level-order.html

C# code:

https://github.com/jianminchen/BTreeLevelOrderTraversal/blob/master/BTreeLevelOrderTraversal5.cs

Solution 5: one queue and iteratively solution (单个queue的迭代解法)
blog:

http://bangbingsyb.blogspot.ca/2014/11/leetcode-binary-tree-level-order.html

C# code:

https://github.com/jianminchen/BTreeLevelOrderTraversal/blob/master/BTreeLevelOrderTraversal6.cs

Solution 6: one queue and extra node null into queue to mark end of level

blog:

http://bangbingsyb.blogspot.ca/2014/11/leetcode-binary-tree-level-order.html

C# code:

https://github.com/jianminchen/BTreeLevelOrderTraversal/blob/master/BTreeLevelOrderTraversal7.cs

Blogs to read:

1. http://www.jiuzhang.com/solutions/binary-tree-level-order-traversal-ii/

2. http://siddontang.gitbooks.io/leetcode-solution/content/tree/binary_tree_level_order_traversal.html

3. http://blog.csdn.net/ljphhj/article/details/22428939