i got WA because i don't realize that

from the upper left to the bottom right
there is no guarantee that they are connected.

I also got WA because of it.
I thought that upper left is
entrance and bottom right is
exit!

Oh, god! You guys are so smart! I ran into the same trap and got AC following your hints.

Thanks a lot!

Yeah I thought same thing!

I also had the same problem, 2 entrance one is upper left, one is lower right, both are open and no wall, :)  (after spending more than 4 hour!)