sudokosolver.java

public class sudokosolver {
    public static void main(String[] args) {
        int[][] sudoku = {
                {5, 0, 0, 0, 0, 3, 0, 8, 0},
                {0, 0, 8, 0, 2, 0, 0, 0, 5},
                {0, 7, 0, 5, 0, 0, 3, 0, 0},

                {0, 5, 0, 7, 0, 1, 0, 0, 6},
                {9, 0, 0, 0, 8, 0, 0, 0, 4},
                {4, 0, 0, 2, 0, 6, 0, 3, 0},

                {0, 0, 7, 0, 0, 9, 0, 4, 0},
                {6, 0, 0, 0, 3, 0, 7, 0, 0},
                {0, 9, 0, 6, 0, 0, 0, 0, 8}
        };
        solver(sudoku , 0);

    }

    private static void solver(int[][] sudoku, int row) {
        if(row == sudoku.length){
            for (int i = 0; i < sudoku.length;i++) {
                for (int j = 0 ; j <sudoku[i].length ; j++) {
                    System.out.print (sudoku[i][j] + "  ");
                }
                System.out.println ();
            }
            System.out.println ("---------------------------------------------------");
            return;
        }

        for (int col = 0 ; col < sudoku.length ; col++){
            if(sudoku[row][col] == 0){

                for (int i = 1; i <= 9 ; i++) {
                    if(issafe(sudoku , row , col , i )){
                        sudoku[row ][col] = i;
                        solver (sudoku , row + 1);
                        sudoku[row][col] = 0;
                    }
                }
                return;

            }
        }

    }

    private static boolean issafe(int[][] sudoku, int row, int col, int val) {

        // Check row
        for (int j = 0; j < 9; j++) {
            if (sudoku[row][j] == val) return false;
        }

        // Check column
        for (int j = 0; j < 9; j++) {
            if (sudoku[j][col] == val) return false;
        }

        // Check 3×3 subgrid
        int sr = (row / 3) * 3;  // starting row of subgrid
        int sc = (col / 3) * 3;  // starting column of subgrid
        for (int k = sr; k < sr + 3; k++) {
            for (int l = sc; l < sc + 3; l++) {
                if (sudoku[k][l] == val) return false;
            }
        }

        return true;
    }

}