This is a fun puzzle, but it's not clear to me how this selects for people with the aptitude to perform well in any particular software development job, as the number of times I've been asked to determine is a string is/contains the concatenation of two dictionary words is I think zero.
Instead of doing stuff like this, you can just give candidates realistic programming challenges and have them write code. You don't even need to be in the room with them; after all, you won't be when they're actually doing the work.
Instead of doing stuff like this, you can just give candidates realistic programming challenges and have them write code. You don't even need to be in the room with them; after all, you won't be when they're actually doing the work.