Question

JAVA PROJECT

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:

Answer 1

Please find my code:

public class SolveSudoku {

   private static final int N = 9;

   public static void main(String[] args) {

       int grid[][] = {{3, 0, 6, 5, 0, 8, 4, 0, 0},

               {5, 2, 0, 0, 0, 0, 0, 0, 0},

               {0, 8, 7, 0, 0, 0, 0, 3, 1},

               {0, 0, 3, 0, 1, 0, 0, 8, 0},

               {9, 0, 0, 8, 6, 3, 0, 0, 5},

               {0, 5, 0, 0, 9, 0, 6, 0, 0},

               {1, 3, 0, 0, 0, 0, 2, 5, 0},

               {0, 0, 0, 0, 0, 0, 0, 7, 4},

               {0, 0, 5, 2, 0, 6, 3, 0, 0}};

       if (solveSudoku(grid)) {

           for (int i = 0; i < N; i++) {

               for (int j = 0; j < N; j++) {

                   System.out.print(grid[i][j] + " ");

               }

               System.out.println();

           }

       }

       else {

           System.out.println("Sudoku can't be solved");

       }

   }

   private static boolean solveSudoku(int[][] grid) {

       RowColumn rowColumn = new RowColumn(0 , 0);

       if (!findUnassignedLocation(grid, rowColumn)) {

           return true;

       }

       for (int num = 1; num <= N; num++) {

           if (isSafe(grid, rowColumn.row, rowColumn.column, num)) {

               grid[rowColumn.row][rowColumn.column] = num;

               if (solveSudoku(grid))

                   return true;

               grid[rowColumn.row][rowColumn.column] = 0;

           }

       }

       return false;

   }

   private static boolean isSafe(int[][] grid, int row, int column, int num) {

       return !usedInRow(grid, row, num) &&

               !usedInColumn(grid, column, num) &&

               !usedInBox(grid, row - row%3, column - column%3, num);

   }

   private static boolean usedInBox(int[][] grid, int boxStartingRow, int boxStartingColumn, int num) {

       for (int row = 0; row < 3; row++) {

           for (int column = 0; column < 3; column++) {

               if (grid[row + boxStartingRow][column + boxStartingColumn] == num)

                   return true;

           }

       }

       return false;

   }

   private static boolean usedInColumn(int[][] grid, int column, int num) {

       for (int row = 0; row < N; row++) {

           if (grid[row][column] == num)

               return true;

       }

       return false;

   }

   private static boolean usedInRow(int[][] grid, int row, int num) {

       for (int column = 0; column < N; column++) {

           if (grid[row][column] == num)

               return true;

       }

       return false;

   }

   private static boolean findUnassignedLocation(int[][] grid, RowColumn rowColumn) {

       for (rowColumn.row = 0; rowColumn.row < N; rowColumn.row++) {

           for (rowColumn.column = 0; rowColumn.column < N; rowColumn.column++) {

               if (grid[rowColumn.row][rowColumn.column] == 0) {

                   return true;

               }

           }

       }

       return false;

   }

   /*

   * Inner class : so that the value of row and column as passed as a reference

   * */

   private static class RowColumn {

       int row;

       int column;

       RowColumn(int row, int column) {

           this.row = row;

           this.column = column;

       }

   }

}

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