Sudoku Puzzle in Java

---

Introduction

Sudoku is a classic puzzle game originating from the 18th century. It traditionally involves a 9x9 grid divided into 3x3 subgrids, where each cell can hold a number between 1 and 9. The objective is to fill all cells with numbers such that no row, column, or subgrid contains duplicate numbers.

In this generalized version, the Sudoku grid has dimensions numRows × numCols, meaning each cell can hold a number between 1 and numRows * numCols. The standard Sudoku rules (no duplicates in rows, columns, and subgrids) still apply.

---

Key Features

1. Dynamic Grid Size: Support for grids of varying sizes such as 2x3, 3x4, etc.
2. Iterative Methods for Solving:
   • Sole Candidate
   • Unique Candidate
   • Duplicate Cells
3. Data Structures:
   • Linked Lists
   • 3D Sparse Table

---

Board Linking Overview

The Sudoku board is constructed using a 3D grid. Each cell within the grid contains possible values, and iterative methods are employed to solve the puzzle by eliminating impossible candidates. Below is a visual representation of the board linking:

Note: Refer to the linked image for details.

---

Class Diagrams

Linked List and Node Classes

The linked list forms the backbone of the data structure for storing cells and their possible values. Each cell is represented as a node, and the linked list enables easy traversal and manipulation of the board's state.

---

Cell, Board, and SudokuSolver Classes

These classes work together to represent the puzzle grid and solve it. Each cell holds potential values, and the SudokuSolver class implements methods to iteratively solve the puzzle.

---

Requirements Before Running Code

1. Java Development Kit (JDK) Installation
   You need to install JDK to compile and run Java code. JDK 17 is recommended. Here are some tutorials to help with setup:

   • Install Java JDK 17 on Windows 11:
     Follow this YouTube tutorial to install JDK 17:
     How to Install Java JDK 17 on Windows 11

   • Setup WSL (Windows Subsystem for Linux) and Run It from Visual Studio Code:
     If you're using WSL, you can run the Ubuntu terminal shell directly from Visual Studio Code. Learn how to set it up using this guide:
     Setup WSL and Run from VS Code

2. Installing Oracle JDK on Windows Subsystem for Linux (WSL)
   If you're working in a WSL environment, follow these steps to install Oracle JDK:

   • Run the WSL terminal as Administrator.

   • Set necessary permissions and variables:

     set -ex
     export JDK_URL=http://download.oracle.com/otn-pub/java/jdk/8u131-b11/d54c1d3a095b4ff2b6607d096fa80163/jdk-8u131-linux-x64.tar.gz
     export UNLIMITED_STRENGTH_URL=http://download.oracle.com/otn-pub/java/jce/8/jce_policy-8.zip

   • Download the JDK and unzip the archive:

     wget --no-cookies --header "Cookie: oraclelicense=accept-securebackup-cookie" ${JDK_URL}
     tar -xzvf jdk-*.tar.gz
     rm -fr jdk-*.tar.gz

   • Move the JDK to the correct directory and configure it:

     sudo mkdir -p /usr/lib/jvm
     sudo mv jdk1.8* /usr/lib/jvm/oracle_jdk8
     wget --no-cookies --header "Cookie: oraclelicense=accept-securebackup-cookie" ${UNLIMITED_STRENGTH_URL}
     unzip jce_policy-8.zip
     mv UnlimitedJCEPolicyJDK8/local_policy.jar /usr/lib/jvm/oracle_jdk8/jre/lib/security/
     mv UnlimitedJCEPolicyJDK8/US_export_policy.jar /usr/lib/jvm/oracle_jdk8/jre/lib/security/

   • Configure alternatives for Java and Javac:

     sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/oracle_jdk8/jre/bin/java 2000
     sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/oracle_jdk8/bin/javac 2000

   • Set environment variables:

     sudo echo "export J2SDKDIR=/usr/lib/jvm/oracle_jdk8
     export J2REDIR=/usr/lib/jvm/oracle_jdk8/jre
     export PATH=$PATH:/usr/lib/jvm/oracle_jdk8/bin:/usr/lib/jvm/oracle_jdk8/db/bin:/usr/lib/jvm/oracle_jdk8/jre/bin
     export JAVA_HOME=/usr/lib/jvm/oracle_jdk8
     export DERBY_HOME=/usr/lib/jvm/oracle_jdk8/db" | sudo tee -a /etc/profile.d/oraclejdk.sh

   Note: You can update the links for other JDK versions if needed.

---

Compilation and Execution

Using the Makefile

A Makefile is provided to streamline the process of compiling and running the Sudoku puzzle in the terminal.

Makefile Commands:

• make: Compiles the .java files.
• make run: Executes the Main class to run the program.
• make clean: Removes all compiled class files and resets the terminal.
• make tar: Compresses the Java files and the Makefile into a .tar.gz archive.
• make unzip: Extracts files from a .tar archive.

default:
	javac *.java

run:
	java Main

clean:
	rm -f *.class
	reset
	clear

tar:
	tar -cvz *.java makefile -f Sudoku.tar.gz

unzip:
	tar -zxvf *.tar

---

Conclusion

This implementation of Sudoku in Java extends the traditional rules of the game to allow for dynamic grid sizes and iterative solving techniques. Using Linked Lists and a 3D Sparse Table as core data structures, the Sudoku puzzle is solved using methods like Sole Candidate and Unique Candidate, ensuring a logical and efficient solution to the puzzle.

Contributing

This project is mainly for educational purposes. However, if you have suggestions or improvements, feel free to open an issue or submit a pull request.

---

License

This project is open source. Please check the repository for more specific license details.