Isn't the use of regexp or regexprep supposed to be limited? It's not that I dislike using it, it's just that these string problems seem to be becoming a regexprep practice.

There's no test case with multiple spaces in the middle. I had considered strjoin(strsplit), which would pass all the tests here if you removed empty cells from the strsplit operation, but it would reduce multiple spaces in the middle to one.

I am sure that there is a more efficient way to perform this operation with just regexp, but the intricacies of this wonderful function still elude me.

works if you have MATLAB >= 2016b

i do not understand what the solution of test 5 should be, or why my solution is wrong

One line

Keeps failing test 5 because pretty much all Matlab functions treat \t as space. Tried strtrim(a), isspace(a(i)) = 1, textscan(a,'%s').
The only thing that picks it up is isequal(a(1),' ') = 0. So, only brute force loop can pass test 5.
Not worth the effort.

Test case 5 is failing for strtrim(str) or isspace(str) functions - both consider \t as space.

Would fail for double spaces within string

Check out the "anchor" expressions $ and ^.

How is this able to pass test 5? It should remove the leading tab and fail.

check the test 5????