力扣 37. 解数独

37. 解数独

编写一个程序，通过填充空格来解决数独问题。

数独的解法需 遵循如下规则：

数字 1-9 在每一行只能出现一次。
数字 1-9 在每一列只能出现一次。
数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。（请参考示例图）
数独部分空格内已填入了数字，空白格用 ‘.’ 表示。

示例 1：

输入：board = [[“5”,“3”,“.”,“.”,“7”,“.”,“.”,“.”,“.”],[“6”,“.”,“.”,“1”,“9”,“5”,“.”,“.”,“.”],[“.”,“9”,“8”,“.”,“.”,“.”,“.”,“6”,“.”],[“8”,“.”,“.”,“.”,“6”,“.”,“.”,“.”,“3”],[“4”,“.”,“.”,“8”,“.”,“3”,“.”,“.”,“1”],[“7”,“.”,“.”,“.”,“2”,“.”,“.”,“.”,“6”],[“.”,“6”,“.”,“.”,“.”,“.”,“2”,“8”,“.”],[“.”,“.”,“.”,“4”,“1”,“9”,“.”,“.”,“5”],[“.”,“.”,“.”,“.”,“8”,“.”,“.”,“7”,“9”]]

输出：[[“5”,“3”,“4”,“6”,“7”,“8”,“9”,“1”,“2”],[“6”,“7”,“2”,“1”,“9”,“5”,“3”,“4”,“8”],[“1”,“9”,“8”,“3”,“4”,“2”,“5”,“6”,“7”],[“8”,“5”,“9”,“7”,“6”,“1”,“4”,“2”,“3”],[“4”,“2”,“6”,“8”,“5”,“3”,“7”,“9”,“1”],[“7”,“1”,“3”,“9”,“2”,“4”,“8”,“5”,“6”],[“9”,“6”,“1”,“5”,“3”,“7”,“2”,“8”,“4”],[“2”,“8”,“7”,“4”,“1”,“9”,“6”,“3”,“5”],[“3”,“4”,“5”,“2”,“8”,“6”,“1”,“7”,“9”]]

解释：输入的数独如上图所示，唯一有效的解决方案如下所示：

提示：

board.length == 9
board[i].length == 9
board[i][j] 是一位数字或者 ‘.’
题目数据 保证 输入数独仅有一个解

class Solution {
    static int sx = 0;
    static int sy = 0;
    static boolean complete = false;

    public void solveSudoku(char[][] board) {
        sx = 0;
        sy = 0;
        complete = false;
        ChangeCell(0, 0, board);
    }

private static void ChangeCell(int row, int cel, char[][] board) {
        if (row >= board.length) complete = true;
        if (cel >= board.length) ChangeCell(row+1, 0, board);
        if (cel >= board.length || row >= board.length) return;

        if (board[row][cel]!='.' ){
            ChangeCell(row, cel+1, board);
        }else{
            for (int i = 1; i <= 9; i++) {
                if (check(row, cel, board, (char)('0'+i))){
                    board[row][cel] = (char)('0'+i);
//                  Print();
                    ChangeCell(row, cel+1, board);
                    if (!complete) board[row][cel] = '.';
                }
            }
        }

    }
    private static boolean check(int row, int cel, char[][] board, char num) {
        for (int i = 0; i < 9; i++) {
            if (board[row][i] == num) return false;
            if (board[i][cel] == num) return false;
        }
        sx = row/3;
        sy = cel/3;
        for (int i = sx*3; i < sx*3+3; i++) {
            for (int j = sy*3; j < sy*3+3; j++) {
                if (board[i][j] == num) return false;
            }
        }
        return true;
    }
}