Coding Challenge
Write the following program in a production programming language of your choice (no Matlab), performing the following in order:
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1. Read rows and columns (cols) as integer arguments from the command line.
2. Create an unsigned char matrix M of size [rows x cols] (if your language of choice doesn't support the unsigned char type, upgrade the type to the shortest integer type supported by that language).
3. Fill M with randomly selected non-negative integers.
4. Apply the filter K=[-1, 0, 1] along the rows axis, then the cols axis (i.e. convolve the matrix M with K along the vertical & horizontal axis respectively).
5. Store the vertical convolution result computed above in a new matrix Dy and the horizontal convolution result in Dx. You must explicitly compute and store the Dy & Dx matrices. 
6. Print the total time taken by the machine in computing Dx and Dy matrices.
7. Compute the min and max values for both Dx & Dy matrices individually (and in separate functions from the above computation of Dx and Dy). Print the computed min & max values.

Requirements:
1. For the definition of convolution, feel free to search internet. Wikipedia is a good starting point resource: https://en.wikipedia.org/wiki/Convolution 
2. After applying the [-1, 0, 1] filter, Dx and Dy must contain the mathematically correct result (i.e. unsigned char requirement is only on input M).
3. If writing in C/C++, the code must be standard compliant with any of the following standard: ANSI C++03,C++11, C++14, C++17, or ANSI C99 or C11.
4. If writing in Python, please do not use standard convolution function. If you use numpy or other scientific library, other than using numpy index operations, don't use any other numpy functions. We are interested in seeing your code/logic rather than the use of standard libraries.
5. The code MUST be optimized primarily for speed (fast execution) and also for efficiency (in terms of memory). 
6. When applying the [-1, 0, 1] filter, in order to achieve the maximum speed up, feel free to assume that this filter or its size NEVER changes.
7. You are free to decide how you want to deal with border conditions. Just explicitly state your assumption in a comment in the solution.
8. Attention to detail in code development is highly valued.