Binary tree root to leaf path minimum path value with the path

Nov. 15, 2017

I like to document my mock interview practice on this algorithm. The topic is about analysis of the algorithm, how to reason to find possible bugs?

Here is C# practice code.  I added line 27 to line 32 to fix the bug since the peer told me that the edge case with no children. The advice from the peer is "After writing the code need to analyze more before running it". 

Story of analysis

I need to explain how the depth first search works since peer asked if I should add an argument of function to pass the existing value. I did explain the algorithm in the mock interview, but the peer felt that he did not know C# very well and got confused. 

I like to write my story to show how I analyze the algorithm after the mock interview, try to make the explanation to a very good one. 

Let us go over  a tree with the following nodes:

      0
  /   |   \
 4   3   6
 /
3

The depth first search algorithm can be solved this way. The root node with value 0 has a tree, to find its minimum path to the leaf node, first if the root node is null, then value is 0; if the root node is not null, and if the root node has no children, it is a base case, the minimum path is the value of root. Otherwise, go over each children of root node with value 0, and go to each child in the array [node 4, node 3, node 6], and ask each node to get its minimum value for the path, denoted as Mi, and just add root node value 0 to Math.Min(Mi, i from 0 to 2).

Miss a base case

From the above paragraph, I highlighted the base case I missed in mock interview using brown color, and the peer had to tell me that there will be a problem if there is no children. In other words, in the tree showing in the above diagram, if the root node with value 0 has no children, it is a base case, the minimum path is the value of root.

Sudoku solver talk

April 11, 2017

Introduction

Sudoku solver is such interesting problem and Julia wrote more than 3 solution in her practice back in 2015. Here is one of the blogs, and also Leetcode 37: sudoku solver is also very good material to review the algorithm.

Sudoku solver talk 

Here is the C# code written in 30 minutes mocking experience.

Transcript is compiled to make it work. C# code is here.

Highlights of a few corrections:

3 nested for loops. The first 2 for loops is to find the first cell with value -1 to do search, try numbers from 1 to 9 and start a DFS search, if all of them are failed, then return false; otherwise return true.

Need to talk about optimization, use the first one with value -1 to start DFS or other cell?

Follow up

Sept. 6, 2017

It is very important to learn the algorithm. Start from code review and learn from the important message in the review.