An epic program written in Racket (close enough to Scheme, and I'm not 20th century enough to know the difference) that either makes sure there's a way to get to the end or actually finds the closest path to it.
If you don't know how to run this, download this repository as a .zip, unzip the file, open main.rkt in DrRacket, and click the Run button with the green play icon triangle.
main.rkt (run this!) creates the GUI, loads the maze file, renders the maze, and calls the step procedure for the two maze solvers.
maze-solver.rkt provides a maze explorer using either a queue or a stack to see if the end can be reached.
a-star.rkt provides an implementation of A* using different heuristic functions.
queue.rkt provides a queue object maker where you take out the item least recently added.
stack.rkt provides a stack object maker where the most recently added item is taken out.
point.rkt provides a point/coordinate/location abstraction.
square.rkt provides a square object maker that represents a tile in a maze from a character. Squares hold data such as the type and the g and cached h scores for A* but do not know their location.
maze.rkt provides a maze object maker that parses plain-text maze data. The default square that is returned with ((maze 'get-square) x y) is a wall if is outside the maze.
square-num.rkt provides a single procedure that performs a complex mathematical operation often used in higher mathematics; see the relevant Wikipedia article here.
Mazes 1 and 2 are from http://nifty.stanford.edu/2008/blaheta-maze/cs2/maze-read.txt
I made maze 3 (I am a world-renowned mazeur, I'll have you know.)
Mazes 4, 6, 7, and 8 are from http://nifty.stanford.edu/2008/blaheta-maze/a-star/a-star.txt
Maze 5 from http://nifty.stanford.edu/2008/blaheta-maze/a-star/screenshot.png
Mazes 9, A, and B are from https://github.com/Sordamente/MazeSolver#test-cases-of-note
Mazes C, D, E, and F are from https://github.com/acrantel/grt-maze-solver/tree/master/src