# How to check if each 3x3 subgrids of sudoku has a valid solution?

**URL:** <https://forum.kirupa.com/t/how-to-check-if-each-3x3-subgrids-of-sudoku-has-a-valid-solution/670244>\
**Category:** programming\
**Created:** [October 16, 2024, 12:58pm UTC](https://forum.kirupa.com/t/how-to-check-if-each-3x3-subgrids-of-sudoku-has-a-valid-solution/670244 "2024-10-16T12:58:40Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![oslon](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/oslon/32/24631_2.png) [@oslon](https://forum.kirupa.com/u/oslon)\
**Post date:** [October 16, 2024, 12:58pm UTC](https://forum.kirupa.com/t/how-to-check-if-each-3x3-subgrids-of-sudoku-has-a-valid-solution/670244/1 "2024-10-16T12:58:40Z")

</div>

```auto
import java.util.*;

public class Example {
    public static void main(String[] args) {
        int[][] solution = {
                {9, 6, 3, 1, 7, 4, 2, 5, 8},
                {1, 7, 8, 3, 2, 5, 6, 4, 9},
                {2, 5, 4, 6, 8, 9, 7, 3, 1},
                {8, 2, 1, 4, 3, 7, 5, 9, 6},
                {4, 9, 6, 8, 5, 2, 3, 1, 7},
                {7, 3, 5, 9, 6, 1, 8, 2, 4},
                {5, 8, 9, 7, 1, 3, 4, 6, 2},
                {3, 1, 7, 2, 4, 6, 9, 8, 5},
                {6, 4, 2, 5, 9, 8, 1, 7, 3}
        };
        boolean ok = true;
        int[] count = new int[9];
        // row-wise loop
        for (int i = 0; i < solution.length; i++) {
            // -1 added for array index starting from 0, means 9 in above means count[8]
            for (int j = 0; j < solution[0].length; j++) {
                count[solution[i][j] - 1]++;
            }
            ok = checkIfOk(count);
            reset(count);

        }
        // column-wise loop
        for (int i = 0; i < solution.length; i++) {
            // -1 added for array index starting from 0, means 9 in above means count[8]
            for (int j = 0; j < solution[0].length; j++) {
                count[solution[j][i] - 1]++;
            }
            ok = checkIfOk(count);
            reset(count);

        }
        System.out.println(ok);

    }

    public static void reset(int[] arr) {
        for (int i = 0; i < arr.length; i++) {
            arr[i] = 0;
        }
    }

    public static boolean checkIfOk(int[] arr) {
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] > 1) {
                return false;
            }
        }
        return true;
    }
}

```

So far, I’ve written to check row and column wise. I also have traced what to do for 3x3 grids.

top left subgrid

i=1-3

j=1-3

top middle subgrid

i=1-3

j=4-6

top right subgrid

i=1-3

j=7-9

middle left subgrid

i=4-6

j=1-3

middle middle subgrid

i=4-6

j=4-6

middle right subgrid

i=4-6

j=7-9

bottom left subgrid

i=7-9

j=1-3

bottom middle subgrid

i=7-9

j=4-6

bottom right subgrid

i=7-9

j=7-9

This is the pattern that I’ve caught. However, I am unable to exactly translate these stuffs to code.

---

<div class="post-metadata">

**Author:** ![oslon](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/oslon/32/24631_2.png) [@oslon](https://forum.kirupa.com/u/oslon)\
**Post date:** [October 16, 2024, 1:18pm UTC](https://forum.kirupa.com/t/how-to-check-if-each-3x3-subgrids-of-sudoku-has-a-valid-solution/670244/2 "2024-10-16T13:18:15Z")

</div>

```auto
        // grid check 3x3
        // 1st grid,2nd grid, 3rd grid
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                count[solution[i][j] - 1]++;
            }
            ok = checkIfOk(count);
            System.out.println(ok);
            reset(count);
            for (int j = 3; j < 6; j++) {
                count[solution[i][j] - 1]++;
            }
            ok = checkIfOk(count);
            System.out.println(ok);
            reset(count);
            for (int j = 6; j < 9; j++) {
                count[solution[i][j] - 1]++;
            }
            ok = checkIfOk(count);
            System.out.println(ok);
            reset(count);
        }

```

I’m near to it. However, this is too long too many lines. I wish there was some sort of logic that I could apply to reduce this without twisting the current logic by a margin.

---

<div class="post-metadata">

**Author:** ![oslon](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/oslon/32/24631_2.png) [@oslon](https://forum.kirupa.com/u/oslon)\
**Post date:** [October 17, 2024, 3:14am UTC](https://forum.kirupa.com/t/how-to-check-if-each-3x3-subgrids-of-sudoku-has-a-valid-solution/670244/3 "2024-10-17T03:14:12Z")

</div>

[https://medium.com/strategio/sudoku-validator-algorithm-dc848cb450934](https://medium.com/strategio/sudoku-validator-algorithm-dc848cb450934)

Found something similar approach. @kirupa sir, please have a look once free