ah yes, I was right. simply string slicing away lines that were checked does make the regex faster. while the code is smaller, it is still slower than the more verbose option. which is only because of the iterative approach of checking each node in the While(True) loop, instead of building 2 lists of lines and manipulating them with .index() and .rindex() [ Paste ]

However, if you notice, even the regex is slower than my iterative approach with index by 3-5 milliseconds. While having one line for the regex is nice, I do think it is harder to read and could prove to be slightly more cumbersome as it could be useless in other types of challenges, while the iterative approach is nice and easily manipulable for most circumstances that may have some quirks.

Also, it shows that the more verbose option is still faster by 7 ms because of the fact that checking each node in the While(True) loop is rather slow approach. So really, there is nothing to it overall, and the main slow down is in you solver that I didn't touch at all, because I wanted to only show the dead end filling part.