How can I perfect out my zigzag matlab function? - matlab

Question

I was given the following Question:
Write a function call zigzag that takes in a 2-dimensional array A and return a 1- dimensional array created by traverse through A in zigzag way starting at position (1,1).
Example:
A =[1 2 3 4 5 6
7 8 9 1 3 4
3 4 5 6 3 1
3 4 5 6 7 8]
zigzag(A) should return:
[1 2 3 4 5 6 4 3 1 9 8 7 3 4 5 6 3 1 8 7 6 5 4 3]
The way I solved it, I am not sure if this is a correct method to do it. I would be glad to know if this is perfect and how I could improve my answer:
function B=zigzag(A)
[r,c]=size(A);
B= reshape(A’,1,:);
m=0
n=0
For r>m+2
m=m+2;
n=n+1;
For i=1:c
B(nc+i)=B(2cn-i+1);
End
End
disp(B)

Answer 1

If it gives you the right output, then you're certainly doing something right. However, what I would have done was access the even rows of your matrix, reverse the directions so that they're displayed in reverse order, transpose your matrix then unravel it.
The reason why we transpose it is because when we unravel a matrix in MATLAB, this means that the columns of the matrix are stacked on top of each other so that one single vector is produced. We want the rows to be stacked on top of each other and making the even rows in reverse order will allow you to do the zigzag that you expect. If you want the rows to be stacked on top of each other, you need to transpose the matrix first so that rows become columns, and when you unravel this matrix, you'll stack the rows on top of each other instead to create a single vector.
Something like this:
B = A; %// Make a copy
B(2:2:end,:) = fliplr(B(2:2:end,:)); %// Flip even rows
B = reshape(B.', 1, []); %// Unravel
With your example, I get:
B =
Columns 1 through 13
1 2 3 4 5 6 4 3 1 9 8 7 3
Columns 14 through 24
4 5 6 3 1 8 7 6 5 4 3