Being an interviewee: Suggest a char with maximum occurrence at the position with the given prefix

May 23, 2018

Introduction

It is my most favorite algorithm to practice with my coach. The algorithm is called to suggest a char with maximum occurrence at the position with the given prefix.

The coached asked me if I have Trie experience two days before my mock interview, so I spent some time to review Leetcode 212 and also my question on stackexchange.com.

The conversation of writing a Trie data structure was very interesting.


Coach: can you explain how you define the Trie?
Julia: It should be recursive structure, Children should have Node type as well.
Coach: Do you need to have a list of numbers for children?
Julia: No. It should be minimum. Every node just takes care of its own number.

In-between the mock interview, the coach asked me why you define the Trie this way, save "ABC" as a member of class definition. I just told the coach that I memorized the solution I reviewed recently. But actually we do not need to do that here. I felt much more relax after we work together more than 10 hours.

Trie algorithm

I learn how to work with the coach and write a solution in the mock interview. And also the coach asked me to test the code using the test case documented from line 93 to line 96, I found the bug on line 107, and delay increment of index variable until line 123.

Here is the transcript of the mock interview.

Follow up 

I wrote the C# code and tested it using a simple test case. Now it is 12:21 AM, I need to rush to go to bed since at tomorrow 8:00 AM I will have a mock interview.

10:00 PM mock interview as interviewer

I also ask the interviewee to work on the algorithm at 10:00 PM mock interview. The intervewee has more than eight years experience working in Silicon Valley to target for biggest software companies, and I helped him to write a Trie solution. What I did is to try to copy my coach, how he did to me. I asked the interviewee to work on the test case, show me the trie, and also give hint to use array for fixed size instead of using Dictionary.

Here is the C# code the interviewee wrote before I write my own C# solution.

Code review from my coach

I sent an email to ask the coach to review my code before I will have next mock interview. The coach offered me to send the code before mocking interview after our second mock interview, so he can prepare better for next mock interview. We can squeeze in more activities in the mock interview together. My coach is super talent programmer and I like his working attitude.

"I think that it is definitely no problem at all. Let us meet Friday morning.

I just like to send you the code I wrote for suggest char based on prefix.

Here is the link."

May 25, 2018
8:00 AM

My coach told me that one thing is not correct. The iterate variable may be null pointer. I need to add null pointer checking on line 152.