CS3243 Assignment 1: 8-Puzzle Solution

Important: Read all the instructions below carefully before you start working on the assignment, and before you make a submission.
• You must do this assignment in groups of two or three (lone-wolves are discouraged). Team members must be from the same tutorial group. Please write the names and matriculation numbers of your team members in the report and the code. Please submit no more than one submission per group.
• Please zip your two python files and report, and submit it via LumiNUS folder.
• The python files’ name should be puzzle A1 xx 1.py and puzzle A1 xx 2.py, your report filename should be report A1 xx.pdf, and the zip file should be name as puzzle A1 xx.zip where xx is your group number (e.g. puzzle A1 03.zip, note that it is 03 and not 3). Please follow the file naming system closely. Points will be deducted for not following the naming convention.
• Kindly check that the submitted code will be able to run on SoC’s Sunfire account. We will be using Sunfire (our UNIX server) to evaluate all submissions.
• Sign up your group on LumiNUS → Class and Groups → Class Groups.
1. Tutorial 2: Groups A1-01 to A1-09 2. Tutorial 3: Groups A1-10 to A1-20 3. Tutorial 4: Groups A1-21 to A1-31 4. Tutorial 5: Groups A1-32 to A1-42 5. Tutorial 6: Groups A1-43 to A1-53 6. Tutorial 7: Groups A1-54 to A1-64 7. Tutorial 8: Groups A1-65 to A1-70
8. Tutorial 9: Groups A1-71 to A1-81
9. Tutorial 10: Groups A1-82 to A1-87
1 Introduction
2 Background
The 8-puzzle is a sliding puzzle that consists of a frame of numbered square tiles in random order with one tile missing. The objective of the puzzle is to arrange the tiles in order by making sliding moves that use the empty space. Figure 1 shows a sample initial state for 8-puzzle.

Figure 1: A sample initial state
3 Problem Statement

Figure 2: Goal state Figure 3: An unsolvable initial state
3.1 Input
The input will be provided in a text file containing three lines to represent the initial state. Each line contains three numbers. They must include the numbers 0–8, where 0 represents the empty space, and 1–8 represents the 8 tiles of the puzzle. For example, the initial state in Figure 1 is encoded in the text file as follows:
0 1 3
4 2 5
7 8 6
3.2 Output
• Your output should be written to a file in the form of a List. If the initial state is Figure 1, one possible output could be [“LEFT”, “UP”, “LEFT”, “UP”]. This will be stored in the file as shown below.
[‘‘LEFT’’, ‘‘UP’’, ‘‘LEFT’’, ‘‘UP’’]
• If the input puzzle is not solvable, output [“UNSOLVABLE”]. Otherwise, output the action of each step. The action could only be “UP”, “DOWN”, “LEFT”, “RIGHT”, to represent the direction of moving the tile towards the space.
• You should ensure each action is valid (e.g., you CANNOT move DOWN when the space is in the first line) and the puzzle should be the same to the goal state after the last action.
4 Submission
Your submissions should contain the following:
• TWO python code files (one for each algorithm), and • ONE report in PDF.
You will lose five points for not submitting either the report or the code files.
4.1 Code
• You are required to implement two different algorithms to solve the puzzle (implemented in two Python files). It is also possible to use the same algorithm but with different heuristics in the implementation.
• Executable: If your program can not be executed, you will get 0 for your code components.
• Correctness: Please make sure your algorithm logic is correct. You will lose mark significantly if you can not pass our test cases.
• Number of moves: Ensure that the solution is within 300 moves.
4.2 Report
Your report must be TYPE-WRITTEN (font size not exceeding 12pt). It should NOT be more than 2 pages.
Your report should contain at least these components:
• Explanation: Explain briefly the algorithms and/or heuristics you used in your solution and why did you choose it.
• Statistics: For the given inputs, please report the following statistics in your report.
– Number of nodes generated.
– Maximum size of the frontier that is reached.
5 FAQ
1. Can we implement the same algorithm? A. No.
2. Can we implement the same algorithm with different heuristic? A. Yes.
A. No, you are free to choose any search algorithm. However, you need to explain the algorithm precisely and concisely in the report.
4. Can we use a different heuristic?
A. Yes, you can! You need to show how it is admissible/consistent/both in the report.
5. Is the page length limitation fixed?
A. Yes. (Sort of!) If the report spans beyond 2 pages, we are not obliged to read the entire report. Grading will be based on the first two pages only. You can use additional pages to include references and algorithm listing (if you want to).
6. How/where do we submit the assignment?
A. We will open up a submission folder on LumiNUS. Only one person from the group has to submit.