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

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 configuration for a sudoku puzzle:

Create a class SudokuPuzzle that has the attributes

• board—a 9 by 9 array of integers that represents the current state of the puzzle, where zero indicates 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 methods:

• 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 initial 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 (zeros)

Explanation / Answer

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;
   }
}

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.