The specification says that where there are multiple valid paths return any of them. Nothing is mentioned about preferring straight lines over diagonals.

After completing this, I get the following:

Test Failed
String lengths are both 11. Strings differ at index 4.
Expected: ".S.\n.P.\n.G."
But was: ".S.\nP..\n.G."

When formatting, this amounts to the following:

Instead of

.S.
.P.
.G.

My code returns

.S.
P..
.G.

Which afaict should be valid?

:O everything is about maintainability! :P

Absolutely, I see the bug now. Thank you for pointing this out. However, the instruction containing 0.55 when code only accepts ints is misleading.

26 letters in English alphabet. Why not return early if the letter is not present?
Ah, I missed that you missed W.

Missed multiple opportunities to return early. The OK variable doesn't need to exist.

Also, your list of characters to split on is not that scalable. That'd be best in a collection of some kind.