Print a given matrix in spiral form

 Problem

Given a 2D array, print it in spiral form.

Input:  {{1,    2,   3,   4},

              {5,    6,   7,   8},

             {9,   10,  11,  12},

            {13,  14,  15,  16 }}

Output: 1 2 3 4 8 12 16 15 14 13 9 5 6 7 11 10 

Explanation: The output is a matrix in a spiral format. 

Input: { {1,   2,   3,   4,  5,   6},

           {7,   8,   9,  10,  11,  12},

          {13,  14,  15, 16,  17,  18}}

Expected output:

1 2 3 4 5 6 12 18 17 16 15 14 13 7 8 9 10 11

Explanation: The output is a matrix in a spiral format.

First, I considered solving this problem by defining the prescriptive rule on which direction to go and how much to go by observing the sample problem. However, I found that the code gets overly complicated if we go that path. 

I decided to think of this problem as the DPS problem where we search through the matrix in a specified direction until we reach the end before switching direction.

This made the problem much easier and I don't have to think about the corner case much.

This can be solved in $O(N * M)$ where N is the width of the matrix and M is the height of the matrix.

UPDATE (2023-03-03): solution in python

Practice statistics:

15 mins: to come up with the algorithm

28 mins: to write the code and review the code.