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For testing the logic of solver() I'd hardcode a maze in the program and not use the huge read and verify code.
Your debug print out could use a lot more data. printing left,right etc doesn't say...

Another suggestion:
Instead of hardcoding "1" all over the program, define a String variable with a meaningful name and use that variable in the code to make it more readable and to allow the...

I don't think your explanation of the logic is correct.
I don't see where you change the location to "-"
I do see where you change a location to an "x"

Your explanation uses code and not words....

Seems like it could be done in one pass.

Can you explain your search algorithm?

Why does the code read the file two times?

Can you explain your search algorithm?

A suggestion for testing: define the maze in a String:


String theMaze =...