解释suduko puzzele的Java代码

Question

我想用Java编写suduko拼图。我已经有了代码，但需要了解一下。

public static void main(String[] args) {
        int[][] arr = { { 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 } };

        int[] rowno = new int[9];
        int[] colno = new int[9];
        int[] sbnos = new int[9];
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                if (arr[i][j] != 0) {
                    makeAchoice(arr, (i * arr.length) + j + 1, rowno, colno, sbnos, arr[i][j]);
                }
            }

        }
        suduko(arr, 1, rowno, colno, sbnos);

    }

    public static void suduko(int[][] arr, int cellno, int[] rownos, int[] colnos, int[] sbnos) {
        if (cellno == 82) {
            for (int i = 0; i < arr.length; i++) {
                for (int j = 0; j < arr.length; j++) {
                    System.out.print(arr[i][j] + " ");
                }
                System.out.println();
            }
            return;
        }
        int rno = (cellno - 1) / arr.length;
        int cno = (cellno - 1) % arr.length;

        if (arr[rno][cno] == 0) {
            int rowno = rownos[rno];
            int colno = colnos[cno];
            int sbno = sbnos[(rno / 3) * 3 + cno / 3];
            int no = rowno | colno | sbno;

            for (int choice = 1; choice <= 9; choice++) {
                if ((no & (1 << choice)) == 0) {
                    makeAchoice(arr, cellno, rownos, colnos, sbnos, choice);
                    suduko(arr, cellno + 1, rownos, colnos, sbnos);
                    unmakeAchoice(arr, cellno, rownos, colnos, sbnos, choice);

                }

            }

        } else {
            suduko(arr, cellno + 1, rownos, colnos, sbnos);
        }

    }

    public static void makeAchoice(int[][] arr, int cellno, int[] rownos, int[] colnos, int[] sbnos, int choice) {
        int rno = (cellno - 1) / arr.length;
        int cno = (cellno - 1) % arr.length;

        arr[rno][cno] = choice;

        rownos[rno] ^= (1 << choice);
        colnos[cno] ^= (1 << choice);
        sbnos[(rno / 3) * 3 + cno / 3] ^= (1 << choice);

    }

    public static void unmakeAchoice(int[][] arr, int cellno, int[] rownos, int[] colnos, int[] sbnos, int choice) {
        int rno = (cellno - 1) / arr.length;
        int cno = (cellno - 1) % arr.length;

        arr[rno][cno] = 0;

        rownos[rno] ^= (1 << choice);
        colnos[cno] ^= (1 << choice);
        sbnos[(rno / 3) * 3 + cno / 3] ^= (1 << choice);

    }