Assignment 01
CENG310
Data Structures and Algorithms with Python
1 Solving Mazes (10 pts)
In this assignment you are expected to develop a Python module, namely maze, that comprises classes and
functions that collectively solves a maze that is represented in a text file. In doing so, you need to follow the
steps that are described in the following sections.
1.1 MazeSolver Class
class MazeSolver()
The module maze should include an implementation for the MazeSolver class. MazeSolver should have the
following data members and methods.
__init__(path)
The constructor will accept a string path and create a Maze instance by utilizing text_to_array method, and
the new Maze instance will be assigned to class member _maze.
_maze
The class member _maze will identify the Maze object for which the solution will be performed.
_cellstack
The class member _cellstack will identify a Stack object onto which maze cell coordinates will be pushed as
tuples of row_index and column_index. As the maze is being explored, the cells to be explored will be pushed
onto the stack. At each exploration iteration, the next cell to be investigated will be read from the top of the
_cellstack with a top operation. If the cell being investigated does not have a valid neighbor, it is popped out
from the _cellstack. At any moment, if the cell at the top position is the exit cell, that means MazeSolver
reached to a solution. On the other hand, if somehow stack becomes empty, this will mean that there is no
solution for the maze.
_explored
_explored will hold the list of the explored cells. For this class member, you may prefer to use a list object.
During the execution of the solution algorithm, this data member will be accessed frequently to check whether
a given cell is visited before.
[Bonus (2.5pts)] As you have already learned, containment checking with a list object takes O(n) time in
the worst case. In order to make these checks, maintain an ordered _explored list and implement a custom
containment check operation that performs a binary search on the list so that this frequent operation can be
done in O(logn).
text_to_array(self, path)
text_to_array should read the file whose path is path and return a Maze object. In order to create a Maze
object, the content of the input text file should be read and a list of lists should be constructed such that it
can be indexed as a two-dimensional array. For example, for a text file such as the one shown below, it should
create and return a list like this: [[’X’,’X’,’S’][’X’,’O’,’O’][’X’,’E’,’X’]] so that it should be able to
be indexed such that, for example, the character at (2,1) would be ‘E’.
[Bonus (1 pt)] Write a single line of code that converts the content of the input file to list of lists. Please
note that obtaining the file handle object should not be included in this one-liner code.
get_a_neighbor(a_tuple)
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Given a tuple of row and column id, get_a_neighbor(a_tuple) computes the location of a valid adjacent up,
right, down, or left cell and returns a coordinate tuple. Valid cells have characters O or E and does not exist in
_explored list.
solve_maze()
solve_maze will provide a solution to the maze which is identified by _maze by adopting the following
algorithm.
1 * Clear and initialize _cellstack and _explored .
2 * Push the starting cell to _cellstack .
3 * As long as _cellstack is not empty , loop :
4 + Get the top cell c from the _cellstack
5 + If c is not in _explored , add c to _explored .
6 + If c is the exit cell , then the maze is solved , quit the algorithm
and return the path ( content of _cellstack ) from start to exit .
7 + Get a neighbor of c that is not visited before and push it to
_cellstack , if there is no such neighbor , pop out c from the
_cellstack .
8 * return [( -1 , -1) ] indicating that there is no solution for the maze .
Also note that, if a solution is found, the list object having the path to the solution should start with the starting
cell coordinates and end with the exit cell coordinates.
1.1.1 Usage of the maze Module
A typical usage of your maze module would be as follows.
1 import maze
2 ms = maze . MazeSolver (’testcase .txt ’)
3 ms . solve_maze ()
4 # Example Output :
5 # [(1 ,0) , (1 ,1) , (2 ,1) , (3 ,1)]
6 # where (1 ,0) is start and (3 ,1) is the end cell
1.2 Maze Class
Build a Maze class that internally maintains a two-dimensional array of characters which represents maze
structure. In such maze representation, there exists four distinct cell types: Moveable cells, walls, starting
point, exiting point.
Maze class should have a constructor accepting a list object satisfying maze structure rules:
• List object has to be comprised of lists of characters.
• It should represent a mxn array where m > 3 and n > 3, and each of the internal lists should be of
length n, and each cell of lists has to hold a single character (technically speaking, they have to be strings
of length one).
• Maze structure have to include only ’O’ (movable path), ’X’ (wall), ’S’ (starting cell), and ’E’ (exit
cell) characters. No other characters should be allowed. There should be exactly one ’S’ and one ’E’
character in the array.
• ’S’ and ’E’ characters should be at the boundry of the maze, in other words, at least one of the
coordinates of cells holding either ’S’ or ’E’ characters has to be either 0, n − 1, or m − 1.
Constructor should accept only those list objects that satisfy these rules, otherwise it should raise an
InvalidMazeException.
Indexing of the maze should start from the upper left corner of the array, in other words, the cell (0,0) should
be the upper left corner of the two-dimensional array.
Maze class should have the following accessor functions.
get_start()
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get_start() should return the starting cell (i.e., a tuple) of the maze. Each cell should be represented as a
tuple (row_index, column_index).
get_exit()
get_exit() should return the list of exit cell (i.e., a tuple) of the maze. Each cell should be represented as a
tuple (row_index, column_index).
1.3 Stack Class
Develop Stack class that implements the Stack ADT that we covered in the lecture. The implementation
provided in the textbook could be adopted.
1.4 Example Test Cases
Below are some of the example text cases that might be helpful to you during the development. Text file
including these examples is available on ODTUClass page. Please note that there will be many more test cases
that we will use during the evaluation of your module.
1.4.1 Test Case 1 (Solution Exists)
1.4.2 Test Case 2 (No Solution Exists)
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1.4.3 Error Cases
2 Delivery Instructions
Please hand in your module as a single file named as maze.py over ODTUClass by 11:59pm on due date.
An Assignment-01 page will be generated soon after the start date of this assignment. Should you have any
questions pertaining to this assignment, please ask them in advance (rather than on the due date) for your
own convenience. Whatever IDE you use, you have to make sure that your module could be run on a Python
interpreter ($> python.exe maze.py) or iPython (%run maze.py).
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