Java Sudoku Generator(easiest solution)

Question

In my last question seen here: Sudoku - Region testing I asked how to check the 3x3 regions and someone was able to give me a satisfactory answer (although it involved a LOT of tinkering to get it working how I wanted to, since they didn't mention what the class table_t was.)

I finished the project and was able to create a sudoku generator, but it feels like it's contrived. And I feel like I've somehow overcomplicated things by taking a very brute-force approach to generating the puzzles.

Essentially my goal is to create a 9x9 grid with 9- 3x3 regions. Each row / col / region must use the numbers 1-9 only once.

The way that I went about solving this was by using a 2-dimensional array to place numbers at random, 3 rows at a time. Once the 3 rows were done it would check the 3 rows, and 3 regions and each vertical col up to the 3rd position. As it iterated through it would do the same until the array was filled, but due to the fact that I was filling with rand, and checking each row / column / region multiple times it felt very inefficient.

Is there an "easier" way to go about doing this with any type of data construct aside from a 2d array? Is there an easier way to check each 3x3 region that might coincide with checking either vert or horizontal better? From a standpoint of computation I can't see too many ways to do it more efficiently without swelling the size of the code dramatically.

Answer 1

I built a sudoku game a while ago and used the dancing links algorithm by Donald Knuth to generate the puzzles. I found these sites very helpful in learning and implementing the algorithm

http://en.wikipedia.org/wiki/Dancing_Links

http://cgi.cse.unsw.edu.au/~xche635/dlx_sodoku/

http://garethrees.org/2007/06/10/zendoku-generation/

Answer 2

import java.util.Random;
import java.util.Scanner;

public class sudoku {

    /**
     * @antony
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int p = 1;
        Random r = new Random();
        int i1=r.nextInt(8);
        int firstval = i1;
        while (p == 1) {
            int x = firstval, v = 1;
            int a[][] = new int[9][9];
            int b[][] = new int[9][9];
            for (int i = 0; i < 9; i++) {
                for (int j = 0; j < 9; j++) {
                    if ((x + j + v) <= 9)
                        a[i][j] = j + x + v;
                    else
                        a[i][j] = j + x + v - 9;
                    if (a[i][j] == 10)
                        a[i][j] = 1;
                    // System.out.print(a[i][j]+" ");
                }
                x += 3;
                if (x >= 9)
                    x = x - 9;
                // System.out.println();
                if (i == 2) {
                    v = 2;
                    x = firstval;
                }
                if (i == 5) {
                    v = 3;
                    x = firstval;
                }

            }
            int eorh;
            Scanner in = new Scanner(System.in);
            System.out
                    .println("hey lets play a game of sudoku:take down the question and replace the 0's with your digits and complete the game by re entering your answer");
            System.out.println("enter your option 1.hard  2.easy");
            eorh = in.nextInt();
            switch (eorh) {
            case 1:
                b[0][0] = a[0][0];
                b[8][8] = a[8][8];
                b[0][3] = a[0][3];
                b[0][4] = a[0][4];
                b[1][2] = a[1][2];
                b[1][3] = a[1][3];
                b[1][6] = a[1][6];
                b[1][7] = a[1][7];
                b[2][0] = a[2][0];
                b[2][4] = a[2][4];
                b[2][8] = a[2][8];
                b[3][2] = a[3][2];
                b[3][8] = a[3][8];
                b[4][2] = a[4][2];
                b[4][3] = a[4][3];
                b[4][5] = a[4][5];
                b[4][6] = a[4][6];
                b[5][0] = a[5][0];
                b[5][6] = a[5][6];
                b[6][0] = a[6][0];
                b[6][4] = a[6][4];
                b[6][8] = a[6][8];
                b[7][1] = a[7][1];
                b[7][2] = a[7][2];
                b[7][5] = a[7][5];
                b[7][6] = a[7][6];
                b[8][4] = a[8][4];
                b[8][5] = a[8][5];
                b[0][0] = a[0][0];
                b[8][8] = a[8][8];

                break;
            case 2:
                b[0][3] = a[0][3];
                b[0][4] = a[0][4];
                b[1][2] = a[1][2];
                b[1][3] = a[1][3];
                b[1][6] = a[1][6];
                b[1][7] = a[1][7];
                b[1][8] = a[1][8];
                b[2][0] = a[2][0];
                b[2][4] = a[2][4];
                b[2][8] = a[2][8];
                b[3][2] = a[3][2];
                b[3][5] = a[3][5];
                b[3][8] = a[3][8];
                b[4][0] = a[4][0];
                b[4][2] = a[4][2];
                b[4][3] = a[4][3];
                b[4][4] = a[4][4];
                b[4][5] = a[4][5];
                b[4][6] = a[4][6];
                b[5][0] = a[5][0];
                b[5][1] = a[5][1];
                b[5][4] = a[5][4];
                b[5][6] = a[5][6];
                b[6][0] = a[6][0];
                b[6][4] = a[6][4];
                b[6][6] = a[6][6];
                b[6][8] = a[6][8];
                b[7][0] = a[7][0];
                b[7][1] = a[7][1];
                b[7][2] = a[7][2];
                b[7][5] = a[7][5];
                b[7][6] = a[7][6];
                b[8][2] = a[8][2];
                b[8][4] = a[8][4];
                b[8][5] = a[8][5];
                break;
            default:
                System.out.println("entered option is incorrect");
                break;
            }

            for (int y = 0; y < 9; y++) {
                for (int z = 0; z < 9; z++) {
                    System.out.print(b[y][z] + " ");
                }
                System.out.println("");
            }
            System.out.println("enter your answer");
            int c[][] = new int[9][9];
            for (int y = 0; y < 9; y++) {
                for (int z = 0; z < 9; z++) {
                    c[y][z] = in.nextInt();
                }
            }
            for (int y = 0; y < 9; y++) {
                for (int z = 0; z < 9; z++)
                    System.out.print(c[y][z] + " ");
                System.out.println();
            }
            int q = 0;
            for (int y = 0; y < 9; y++) {
                for (int z = 0; z < 9; z++)
                    if (a[y][z] == c[y][z])
                        continue;
                    else {
                        q++;
                        break;
                    }
            }
            if (q == 0)
                System.out
                        .println("the answer you have entered is correct well done");
            else
                System.out.println("oh  wrong answer better luck next time");
            System.out
                    .println("do you want to play a different game of sudoku(1/0)");
            p = in.nextInt();
            firstval=r.nextInt(8);
            /*if (firstval > 8)
                firstval -= 9;*/
        }

    }
}