How to create subgrids & dividers in Sudoku program Java?

Question

I am creating a Sudoku helper program, where I help the user solve the puzzle.

How can I create horizontal " = " and vertical "| " dividers in order to break up the grid into subgrids? For the horizontal dividers, for the outer (row) loop, the dividing line is added after rows 2 and 5. For vertical dividers, inner (cols) loop, add vertical bar " | " after cols 2 and 5.

Lastly, how can I create headers to each row and column in order for the user to identify each row and cols by its id?

public class Sudoku {
   public static int rows = 9;
   public static int cols = 9;
   public static int[][] board = new int[rows][cols];

   public static void show() {
   for (int rows=1; rows<board.length; rows++) {
         for (int cols=1; cols<board.length; cols++) {
         board[rows][cols] = '0';
      }
   } 
}
   public static void main(String[] args) {
   //print out the contents of board array
      int board[][] = new int[9][9];

      for (int rows = 0; rows < 9; rows++) {
         for (int cols = 0; cols < 9; cols++) {
         System.out.print(board [rows][cols] + " ");
         }

         System.out.println("");
      }
      show();


   }
}

The output of my program:

0 0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0

Answer 1

This is something I wrote some time ago, just change the sudoku array to your arrayname ( board ).

for(int x = 0; x < 9; x++){
        System.out.print("|     |     |     ||     |     |     ||     |     |     |\n");
        for(int y = 0; y < 9; y++){
            if(y == 0 || y == 3 || y == 6) System.out.print("|");
            System.out.print("  " + sudoku[x][y] + "  |");
        }
        System.out.print("\n");     
        System.out.print("|     |     |     ||     |     |     ||     |     |     |\n");
        if(x == 2 || x == 5)
            System.out.print("=========================================================");
        else
            System.out.print("---------------------------------------------------------");
        System.out.print("\n");
    }

This will create something like this:

---------------------------------------------------------
|     |     |     ||     |     |     ||     |     |     |
|  0  |  0  |  0  ||  0  |  0  |  0  ||  0  |  0  |  0  |
|     |     |     ||     |     |     ||     |     |     |
---------------------------------------------------------
|     |     |     ||     |     |     ||     |     |     |
|  0  |  0  |  8  ||  0  |  6  |  5  ||  0  |  0  |  0  |
|     |     |     ||     |     |     ||     |     |     |
---------------------------------------------------------
|     |     |     ||     |     |     ||     |     |     |
|  0  |  3  |  0  ||  9  |  0  |  4  ||  5  |  0  |  8  |
|     |     |     ||     |     |     ||     |     |     |
=========================================================
|     |     |     ||     |     |     ||     |     |     |
|  0  |  0  |  0  ||  0  |  2  |  0  ||  4  |  5  |  0  |
|     |     |     ||     |     |     ||     |     |     |
---------------------------------------------------------
|     |     |     ||     |     |     ||     |     |     |
|  0  |  0  |  0  ||  0  |  0  |  0  ||  0  |  0  |  6  |
|     |     |     ||     |     |     ||     |     |     |
---------------------------------------------------------
|     |     |     ||     |     |     ||     |     |     |
|  0  |  0  |  7  ||  0  |  0  |  0  ||  3  |  0  |  0  |
|     |     |     ||     |     |     ||     |     |     |
=========================================================
|     |     |     ||     |     |     ||     |     |     |
|  1  |  2  |  0  ||  0  |  4  |  6  ||  0  |  7  |  0  |
|     |     |     ||     |     |     ||     |     |     |
---------------------------------------------------------
|     |     |     ||     |     |     ||     |     |     |
|  0  |  0  |  3  ||  0  |  8  |  0  ||  1  |  0  |  0  |
|     |     |     ||     |     |     ||     |     |     |
---------------------------------------------------------
|     |     |     ||     |     |     ||     |     |     |
|  6  |  0  |  0  ||  7  |  5  |  0  ||  0  |  0  |  0  |
|     |     |     ||     |     |     ||     |     |     |
---------------------------------------------------------

Answer 2

A bit ugly, but you can definitely improve it:

public static void main(String[] args) {
  //print out the contents of board array
  int board[][] = new int[9][9];
  System.out.println("  0 1 2 | 3 4 5 | 6 7 8 <-- column id");      
  System.out.println("========================  v- row id");
  for (int rows = 0; rows < 9; rows++) {
     for (int cols = 0; cols < 9; cols++) {    
         if (cols % 3 == 0) {
             System.out.print("| ");
         }
        System.out.print(board [rows][cols] + " ");            
     }         

     System.out.println("| "+ rows);
     if ((rows+1) %3 == 0) {
         System.out.println("========================");
     } 
  }
  show();


}

It shows something like that:

  0 1 2 | 3 4 5 | 6 7 8 <-- column id
========================  v- row id
| 0 0 0 | 0 0 0 | 0 0 0 | 0
| 0 0 0 | 0 0 0 | 0 0 0 | 1
| 0 0 0 | 0 0 0 | 0 0 0 | 2
========================
| 0 0 0 | 0 0 0 | 0 0 0 | 3
| 0 0 0 | 0 0 0 | 0 0 0 | 4
| 0 0 0 | 0 0 0 | 0 0 0 | 5
========================
| 0 0 0 | 0 0 0 | 0 0 0 | 6
| 0 0 0 | 0 0 0 | 0 0 0 | 7
| 0 0 0 | 0 0 0 | 0 0 0 | 8
========================

UPDATE : If you want the row id at the beginning of each line, then do the following:

public static void main(String[] args) {
    //print out the contents of board array
    int board[][] = new int[9][9];
    System.out.println("   0 1 2   3 4 5   6 7 8");      
    System.out.println("  ========================");
    for (int rows = 0; rows < 9; rows++) {
          System.out.print(rows+" |");
         for (int cols = 0; cols < 9; cols++) {             
            System.out.print(board [rows][cols] + " ");            
            if ((cols+1) % 3 == 0) {
                 System.out.print("| ");
            }
         }         

         System.out.println();
         if ((rows+1) %3 == 0) {
             System.out.println("  ========================");
         } 
     }
     show();
}

It will show:

   0 1 2   3 4 5   6 7 8
  ========================
0 |0 0 0 | 0 0 0 | 0 0 0 | 
1 |0 0 0 | 0 0 0 | 0 0 0 | 
2 |0 0 0 | 0 0 0 | 0 0 0 | 
  ========================
3 |0 0 0 | 0 0 0 | 0 0 0 | 
4 |0 0 0 | 0 0 0 | 0 0 0 | 
5 |0 0 0 | 0 0 0 | 0 0 0 | 
  ========================
6 |0 0 0 | 0 0 0 | 0 0 0 | 
7 |0 0 0 | 0 0 0 | 0 0 0 | 
8 |0 0 0 | 0 0 0 | 0 0 0 | 
  ========================