COMP9021 Principles of Programming 
Term 2, 2024 
Assignment 2 
Worth 13marks and due Week 11 Monday @ 10am 
1. General Matters 
 
1.1 Aim 
The purpose of this assignment is to: 
• Develop your problem-solving skills. 
• Design and implement the solution to a problem in the form of a medium sized Python program. 
• Analyse the various features of a labyrinth, represented by a particular coding of its basic elements 
into numbers, from the set {0, 1, 2, 3} only, stored in a text file. 
• Check that the input text file is correct and represents a labyrinth. 
• Output the labyrinth features nicely. 
• Use object-oriented programming. 
 
1.2 Marking 
This assignment is worth 13 marks distributed as follows: 
 2 
 
 
Your program will be tested against several inputs. For each test, the auto-marking script will let your 
program run for 30 seconds. The outputs of your program should be exactly as indicated. 
 
1.3 Due Date and Submission 
Your programs will be stored in a file named labyrinth.py. The assignment can be submitted more than 
once. The last version just before the due date and time will be marked (unless you submit late in which 
case the last late version will be marked). 
Assignment 2 is due Week 11 Monday 5 August 2024 @ 10:00am (Sydney time). 
Please note that late submission with 5% penalty per day is allowed up to 5 days from the due date, that 
is, any late submission after Week 11 Saturday 10 August 2024 @ 10:00am will be discarded. 
Please make sure not to change the filename labyrinth.py while submitting by clicking on [Mark] button in 
Ed. It is your responsibility to check that your submission did go through properly using Submissions link in 
Ed otherwise your mark will be zero for Assignment 2. 
 
1.4 Reminder on Plagiarism Policy 
You are permitted, indeed encouraged, to discuss ways to solve the assignment with other people. Such 
discussions must be in terms of algorithms, not code. But you must implement the solution on your own. 
Submissions are scanned for similarities that occur when students copy and modify other people’s work or 
work very closely together on a single implementation. Severe penalties apply. 
 
2. Description 
The representation of the labyrinth is based on a coding with only the four digits 0, 1, 2 and 3 such that: 
 
• 0 codes points that are connected to neither their right nor their below neighbours: 
• 1 codes points that are connected to their right neighbours but not to their below ones: 
• 2 codes points that are connected to their below neighbours but not to their right ones: 
• 3 codes points that are connected to both their right and below neighbours: 
 
A point that is connected to none of their left, right, above, and below neighbours represents a pillar: 
 
Analysing the labyrinth will also allow to represent: 
 
• cul-de-sac: 
• entry-exit path: 
 3 
 
 
3. Examples 
 
3.1 First Example 
The file named labyrinth_1.txt contains the following: 
 
1 0 2 2 1 2 3 0 
3 2 2 1 2 0 2 2 
3 0 1 1 3 1 0 0 
2 0 3 0 0 1 2 0 
3 2 2 0 1 2 3 2 
1 0 0 1 1 0 0 0 
 
As per the coding above, labyrinth_1.txt will look like the following: 
 
 
Here is a possible interaction: 
 4 
 
 
3.2 Second Example 
The file named labyrinth_2.txt contains the following: 
 
022302120222 
222223111032 
301322130302 
312322232330 
001000100000 
 
As per the coding above, labyrinth_2.txt will look like the following: 
 
 
 
Here is a possible interaction: 
 
 
 
 5 
 
 
3.3 Third Example 
The file named labyrinth_3.txt contains the following: 
 
31111111132 
21122131202 
33023022112 
20310213122 
31011120202 
21230230112 
30223031302 
03122121212 
22203110322 
22110311002 
11111101110 
 
As per the coding above, labyrinth_3.txt will look like the following: 
 
Here is a possible interaction: 
 6 
 
 
3.4 Fourth Example 
The file named labyrinth_4.txt contains the following: 
 
111120 
112020 
002020 
002010 
001110 
 
As per the coding above, labyrinth_4.txt will look like the following: 
 
 
 
Here is a possible interaction: 
 
 
 
 7 
 
 
3.5 Fifth Example 
The file named labyrinth_5.txt contains the following: 
 
 1 1 2 
 1 12 
 
 1 1 0 
 
 
As per the coding above, labyrinth_5.txt will look like the following: 
 
 
 
Here is a possible interaction: 
 
 
 
 8 
 
 
3.6 Sixth Example 
The file named labyrinth_6.txt contains the following: 
 
0111221210021212201201323330200 
1131011210301210323130331302310 
3300200323203011010332232320332 
2330312230220302032203223112310 
1211020213223110101302032332212 
1112222331300131013312312223130 
1110120222130303102210113130100 
0020320223200020113011131202302 
3213100301021111202122030110112 
1200320130030313001031302312110 
0310130300203000312021011212020 
3131210323320222322212332031120 
2021033213003230103112331130222 
1013300313133312220131222100010 
1231322020123133221023110302002 
3322231133223020311032001102310 
2323101332332011010132023031132 
2200112102133112231003320012120 
2130210032120230313010200102112 
2311003320123302322223032120112 
0201320233130133202333323012120 
1003010311132003122332112221132 
2032100103021312110202200332310 
3211202310233321202022122021022 
1200330103010322222131033003000 
1121200200313110310030131100332 
0012021023310003332301123031222 
0120302110232113312232012023020 
2303222021330232031311210131312 
0101112200130031003120203121102 
2012100113233120321011002012220 
0010322001332202013202312122110 
0213000131303132112301110130112 
1222303101032032301032210302110 
1220131300113200003021222120012 
1333010013001231321110022323022 
3021223221133030131221100102210 
2013320130211320203021000311312 
0303003010033021320232203222020 
2030233001202311110121110133220 
1001011011001101100000010100100 
 9 
 
 
As per the coding above, labyrinth_6.txt will look like the following: 
 
 10 
 
 
Here is a possible interaction: 
 
 
 
 11 
 
 
4. Detailed Description 
 
4.1 Input 
The input is expected to consist of ydim lines of xdim members of {0, 1, 2, 3}, where x dim and ydim are at least 
equal to 2 and at most equal to 31 and 41, respectively, with possibly lines consisting of spaces only that 
will be ignored and with possibly spaces anywhere on the lines with digits. 
The xth digit n of the yth line, with 0 ≤ x < xdim and 0 ≤ y < ydim, is to be: 
• associated with a point situated x * 0.5 cm to the right and y * 0.5 cm below an origin, 
• connected to the point 0.5 cm to its right if n = 1 or n = 3, and 
• connected to the point 0.5 cm below itself if n = 2 or n = 3. 
The last digit on every line with digits (that is, not on blank lines) cannot be equal to 1 or 3, and the digits 
on the last line with digits cannot be equal to 2 or 3, which ensures that the input encodes a labyrinth, 
that is, a grid of width (xdim - 1) * 0.5 cm and of height (ydim - 1) * 0.5 cm (hence of maximum width 15 cm 
and of maximum height 20 cm), with possibly gaps on the sides and inside. 
A point not connected to any of its neighbours is thought of as a pillar and a point connected to at least 
one of its neighbours is thought of as part of a wall. 
We talk about inner point to refer to a point that lies (x + 0.5) * 0.5 cm to the right of and (y + 0.5) * 0.5 
cm below the origin with 0 ≤ x < xdim - 1 and 0 ≤ y < ydim - 1. 
Practically, the input will be stored in a text file as shown in the six examples above. The program will exit 
immediately if the input is not as expected. 
 
4.2 Output 
Consider executing from the Python prompt the statement from labyrinth import * followed by the 
statement lab = Labyrinth(filename). In case filename does not exist in the working directory, then Python 
will raise a FileNotFoundError exception, that does not need to be caught. Assume that filename does 
exist (in the working directory). If the input is incorrect in that it does not contain only digits in {0, 1, 2, 3} 
besides spaces, or in that it contains either too few or too many nonblank lines, or in that some nonblank 
lines contain too many or too few digits, or in that two of its nonblank lines do not contain the same 
number of digits, then the effect of executing lab = Labyrinth(filename) should be to generate a 
LabyrinthError exception that reads: 
 
 
 12 
 
 
If the previous conditions hold but the further conditions spelled out above for the input to qualify as a 
labyrinth (that is, the condition on the last digit on every line with digits and the condition on the digits on 
the last line) do not hold, then the effect of executing lab = Labyrinth(filename) should be to generate a 
LabyrinthError exception that reads: 
 
 
 
If the input is correct and represents a labyrinth, then lab = Labyrinth(filename) followed by 
lab.display_features() should have the effect of outputting the following: 
1. the number of gates, that is, the number of consecutive points on one of the four sides of the 
labyrinth that are not connected, 
2. the number of sets of connected walls, 
3. the number of inner points that cannot be accessed from any gate, starting from the point in the 
middle of a gate and going from inner points to neighbouring inner points, 
4. the number of maximal areas that can be accessed from at least one gate (the number of 
accessible inner points is at most equal to the number of gates), 
5. the number of accessible cul-de-sacs (a cul-de-sac is a maximal set S of connected inner points that 
can all be accessed from the same gate g and such that for all points p in S, if p has been accessed 
from g for the first time, then either p is in a dead end or moving on without ever getting back 
leads into a dead end), and 
6. the number of entry-exit paths with no intersections not to cul-de-sacs consisting of a maximal set 
S of connected inner points that go from a gate to another (necessarily different) gate and such that 
for all points p in S, there is only one way to move on from p without getting back and without 
entering a cul-de-sac, in other words, the resulting path is choice-free, that is, such that leaving the 
path, at any inner point where that is possible, immediately leads into a cul-de-sac. 
 
The above should be displayed exactly as described below. 
A first line that reads one of: 
The labyrinth has no gate. 
The labyrinth has a single gate. 
The labyrinth has N gates. 
with N an appropriate integer at least equal to 2. 
 13 
 
 
A second line that reads one of: 
The labyrinth has no wall. 
The labyrinth has walls that are all connected. 
The labyrinth has N sets of walls that are all connected. 
with N an appropriate integer at least equal to 2. 
 
A third line that reads one of: 
The labyrinth has no inaccessible inner point. 
The labyrinth has a unique inaccessible inner point. 
The labyrinth has N inaccessible inner points. 
with N an appropriate integer at least equal to 2. 
 
A fourth line that reads one of: 
The labyrinth has no accessible area. 
The labyrinth has a unique accessible area. 
The labyrinth has N accessible areas. 
with N an appropriate integer at least equal to 2. 
 
A fifth line that reads one of: 
The labyrinth has no accessible cul-de-sac. 
The labyrinth has accessible cul-de-sacs that are all connected. 
The labyrinth has N sets of accessible cul-de-sacs that are all connected. 
with N an appropriate integer at least equal to 2. 
 
A sixth line that reads one of: 
The labyrinth has no entry-exit path with no intersection not to cul-de-sacs. 
The labyrinth has a unique entry-exit path with no intersection not to cul-de-sacs. 
The labyrinth has N entry-exit paths with no intersections not to cul-de-sacs. 
with N an appropriate integer at least equal to 2. 
 
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