A possible solution outline:

• Create a Stack to hold grid positions - Stack<Position>

• Check that the starting position is not blocked!

• Set the current position to the starting position and push each immediate neighbor on the stack provided that neighbor is not already marked.

• While the current position is not the finish position and the stack is not empty

  1. pop the top position off the stack

  2. If the position is not marked, make it the current position, mark it and add its unmarked neighbors to the stack.

• If current is NOT the finish position, there is no path from the start to the finish.