Introduction
It is so enjoyable to write sudoku solver as a depth first solution and also walk through each step called "thinking out loud". The conversation after the mocking this evening starting from 10:00 pm until 11:30 pm is also rewarding experience, I try to contribute my two cents for a young person to prepare for an important trial. Although I have written sudoku solver solution over 5 times last 3 months, I still found that this time I wrote a different style.
Algorithm practice
Here is my C# practice. No bug in the first writing, only fix two compiler errors, pass all test cases the first time.
I forgot that I need to visit current node instead of using two loops to scan the matrix to find the first empty element. After 1 - 2 minutes, I noticed the issue, and then I corrected my thought process and continue to write from line 25.
I wrote line 38 and thought out loud saying that it is kind of stupid to write '1', '2' to '9', actually I am thinking that it is better to split from string "123456789" instead of declaring a char array.
After the mocking interview
I spent over 20 minutes to share my past 80 interviews with the peer, what I have learned through the mocking practice, specially how I learn to write sudoku algorithm through more than three practices.
One thing I like to say is that if you take it slow, you have a lot of time to write code in 30 minutes mocking interview; but if you write in a rush, then you end up with issues. I am getting more comfortable to stay on one node at a time.
The fact is that in my solution there is no need to write a double for loop at all. Avoid scan from top to down by row, left to right by column to find the first empty element all the time.
The peer gave me the feedback saying that I did very good to explain the algorithm by going over the example to find options 1, 2, 4, 7 ( see line 117 - line 124).
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