Sudoku is a popular logic puzzle that uses a 9 by 9 array of squares that are or

ID: 3687149 • Letter: S

Question

Sudoku is a popular logic puzzle that uses a 9 by 9 array of squares that are organized into 3 by 3 subarrays. The puzzle solver must fill in the squares with the digits 1 to 9 such that no digit is repeated in any row, any column, or any of the nine 3 by 3 subgroups of squares. Initially, some squares are filled in already and cannot be changed. For example, the following might be a starting congiguration for a Sudoku puzzle:

Create a class sudokuPuzzle that has the attributes

board- a 9 by 9 array of integers that represents the curretn state of the puzzle, where 0 indicate a blank square

start- a 9 by 9 array of boolean values that indicates which squares in board are given values that cannot be changed

and the following methiods:

sudokupuzzle- a constructor that creates an empty puzzle

toString- returns a string representation of the puzzle that can be printed

addInitial(row,col, value)- sets the given square to the given value as an inital value that cannot be changed by the puzzle solver

addGuess(row,col,value)-sets the given square to the given value; the value can be changed later by another call to addGuess

checkPuzzle- returns true if the values in the puzzle do not violate the restrictions

getValueIn(row,col)- returns the value in the given square

getAllowedValues(row, col)- returns a one dimensional array of nine booleans, each of which corresponds to a digit and is true if the digit can be placed in the given square without violating the restrictions

isFull- returns true if every square has a value

reset- changes all of the nonpermanent squares back to blanks(0s)

Write a main method in the class Sudoku that creates a SudokuPuzzle obkect and sets its initial configuration. Then use a loop to allow someone to play Sudoku. Display the current configuration and ask for a row, column, and value. Update the game board and display it again. If the configuration does not satisfy the restrictions, let the user know. Indicate when the puzzle has been solved correctly. In that case, both checkPuzzle and isFull would return true. You should also allow options for resetting the puzzle and displaying the values that can be placed in a given square.

Explanation / Answer

Sudoku.java

import java.util.Scanner;

public class Sudoku
{

    public static void main(String[] args)
    {

       Scanner reader = new Scanner(System.in);
       System.out.println("Sudoku Game: ");
       SudokuPuzzle puzzle = new SudokuPuzzle();
       puzzle.initializePuzzle(puzzle);
       System.out.print("The puzzle is: " + puzzle);
       boolean done = false;
       while(!done)
       {
           System.out.println("What would you like to do? " + "Clear puzzle(C) Set a square (S) Get possible values (G) Quit (Q)");
           String response = reader.next();
           response = response.toLowerCase();
           if(response.equals("q"))
           {
               System.out.println("Thanks for playing.");
               done = true;
           }
           else if(response.equals("s"))
           {
               System.out.println("Which row (1-9) and column (1-9) do you want to change?");
               int row = reader.nextInt()-1;
               int col = reader.nextInt()-1;
               System.out.println("What should the value (1-9) be?");
               int value = reader.nextInt();
               puzzle.addGuess(row, col, value);
           }
           else if(response.equals("g"))
           {
               System.out.println("Which row (1-9) and column (1-9) do you   want to get values for?");
               int row = reader.nextInt()-1;
               int col = reader.nextInt()-1;

               boolean valid[] = puzzle.getAllowedValues(row, col);
               System.out.print("Allowed values are: ");
               for(int i=0; i<9; i++)
               {
                   if(valid[i])
                       System.out.print((i+1)+ " ");
               }
                   System.out.println();
           }
           else if(response.equals("c"))
           {
                       puzzle.reset();
           }
           System.out.print("The puzzle is now: " + puzzle);
           if(!puzzle.checkPuzzle())
                   System.out.println("You have made an error in the puzzle.");
               else if(puzzle.isFull())
                   System.out.println("Congratulations, you have completed the puzzle.");
       }
   }

}

SudokuPuzzle.java

import java.util.Scanner;

public class SudokuPuzzle
{

   private int board [][];
   private int start[][];

   public SudokuPuzzle()
   {
       start = new int [9][9];
       board = new int [9][9];
   }

   public String toString()
   {
       String puzzleString = "Row/Col     1 2 3 4 5 6 7 8 9 ";
       puzzleString = puzzleString+ "   -------------------------- ";

       for (int i=0; i<9; i++)
       {
           puzzleString = puzzleString + (i+1) + " |";
           for (int j=0; j<9; j++)
           {
               if (board [i][j] == 0)
                   puzzleString = puzzleString + " " + ".|";
               else
                   puzzleString = puzzleString + " " +board [i][j] + "|";
           }
           puzzleString = puzzleString + " ";
           puzzleString = puzzleString + " |__|__|__|__|__|__|__|__|__| ";
       }

       return puzzleString;
   }

   public void addInitial(int row, int col, int value)
   {
       if (row>=0 && row<=9 && col >=0 && col <=9 && value >=1 && value <=9){
           start [row][col] = value;
           board [row][col] = value;
       }
   }

   public void addGuess(int row, int col, int value)
   {
       // only set the value if the start is 0
       if (row>=0 && row<=9 && col >=0 && col <=9 && value >=1 && value <=9 && start [row][col] == 0)
       {
           board [row][col]= value;
       }
   }

   public int getValueIn(int row, int col)
   {
       return board[row][col];
   }

   public void reset()
   {
       for (int i=0;i<9;i++)
           for( int j=0;j<9;j++)
               board[i][j] = start[i][j];
   }

   public boolean isFull()
   {
       boolean allFilled = true;
       for (int i=0;i<9;i++)
           for( int j=0;j<9;j++)
               allFilled = allFilled && board[i][j]>0;
       return allFilled;
   }

   public boolean[] getAllowedValues(int row, int col)
   {
       // save the value at the location, thren try all 9 values
       int savedValue = board[row][col];
       boolean result[] = new boolean[9];
       for (int value = 1; value <=9; value++)
       {
           board [row][col] = value;
           result[value-1] = checkPuzzle();
       }
       board [row][col] = savedValue;
       return result;
   }

   public boolean checkPuzzle()
   {
       boolean looksGood = true;
       for (int i=0;i<9;i++)
       {
           looksGood = looksGood && checkRow(i);
           looksGood = looksGood && checkCol(i);
           looksGood = looksGood && checkSub(i);
       }
       return looksGood;
   }

   public boolean checkRow(int row)
   {
       int count[]= new int[10];
       for (int col=0;col<9;col++)
       {
           count[board[row][col]]++;
       }
       boolean countIsOk = true;

       for(int i=1; i<=9; i++)
           countIsOk = countIsOk && (count[i]<=1);
       return countIsOk;

   }

   public boolean checkCol(int col)
   {
       int count[] = new int[10];
       for(int row=0; row<9; row++)
       {
           count[board[row][col]]++;
       }
       boolean countIsOk = true;
       for(int i=1; i<=9; i++)
           countIsOk = countIsOk && (count[i]<=1);
       return countIsOk;
   }

   public boolean checkSub(int sub)
   {
       int count[] = new int[10];
       int rowBase = (sub/3) *3;

       // The above will give 0, 3, or 6 because of integer division
       int colBase = (sub%3) *3;
       for(int i=0; i<3; i++)
       {
           for(int j=0; j<3; j++)
           {
               count[board[rowBase+i][colBase+j]]++;
           }
       }

       boolean countIsOk = true;
       for(int i=1; i<=9; i++)
           countIsOk = countIsOk && (count[i]<=1);
       return countIsOk;
   }

   public static void initializePuzzle(SudokuPuzzle p)
   {
   p.addInitial(0,0,1);
   p.addInitial(0,1,2);
   p.addInitial(0,2,3);
   p.addInitial(0,3,4);
   p.addInitial(0,4,9);
   p.addInitial(0,5,7);
   p.addInitial(0,6,8);
   p.addInitial(0,7,6);
   p.addInitial(0,8,5);
   p.addInitial(1,0,4);
   p.addInitial(1,1,5);
   p.addInitial(1,2,9);
   p.addInitial(2,0,6);
   p.addInitial(2,1,7);
   p.addInitial(2,2,8);
   p.addInitial(3,0,3);
   p.addInitial(3,4,1);
   p.addInitial(4,0,2);
   p.addInitial(5,0,9);
   p.addInitial(5,5,5);
   p.addInitial(6,0,8);
   p.addInitial(7,0,7);
   p.addInitial(8,0,5);
   p.addInitial(8,3,9);
   }
}

sample output

Sudoku Game:
The puzzle is:
Row/Col
    1 2 3 4 5 6 7 8 9
   --------------------------
1 | 1| 2| 3| 4| 9| 7| 8| 6| 5|
|__|__|__|__|__|__|__|__|__|
2 | 4| 5| 9| .| .| .| .| .| .|
|__|__|__|__|__|__|__|__|__|
3 | 6| 7| 8| .| .| .| .| .| .|
|__|__|__|__|__|__|__|__|__|
4 | 3| .| .| .| 1| .| .| .| .|
|__|__|__|__|__|__|__|__|__|
5 | 2| .| .| .| .| .| .| .| .|
|__|__|__|__|__|__|__|__|__|
6 | 9| .| .| .| .| 5| .| .| .|
|__|__|__|__|__|__|__|__|__|
7 | 8| .| .| .| .| .| .| .| .|
|__|__|__|__|__|__|__|__|__|
8 | 7| .| .| .| .| .| .| .| .|
|__|__|__|__|__|__|__|__|__|
9 | 5| .| .| 9| .| .| .| .| .|
|__|__|__|__|__|__|__|__|__|

What would you like to do?
Clear puzzle(C) Set a square (S) Get possible values (G) Quit (Q)
S
Which row (1-9) and column (1-9) do you want to change?
2 2
What should the value (1-9) be?
5

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