数独

https://leetcode.com/problems/sudoku-solver/

1.输入9*9的矩阵，有数字的地方是数字，没数字的地方显示'.'
2.从第一行开始每一行遍历每一个格子，当碰到'.'的时候，需要再这个格子填入数字
3.怎么填数字？ 从1到9 一个一个试

   public void solveSudoku(char[][] board) {
        this.solvehelper(board, 0, 0);
    }

    public Boolean solvehelper(char[][] board, int i, int j) {
        if (i == 9) {
            return true;
        }

        if (j >= 9) {
            return solvehelper(board, i + 1, 0);
        }

        if (board[i][j] != '.') {
            return solvehelper(board, i, j + 1);
        }

        for (char c = '1'; c <= '9'; c++) {
            if (!suduValiad(board, i, j, c)) {
                continue;
            }

            board[i][j] = c;

            if (solvehelper(board, i, j + 1)) {
                return true;
            }
            board[i][j] = '.';
        }
        return false;
    }

    public Boolean suduValiad(char[][] board, int i, int j, char val) {
        for (int x = 0; x < 9; x++) {
            if (board[x][j] == val) {
                return false;
            }
        }

        for (int y = 0; y < 9; y++) {
            if (board[i][y] == val) {
                return false;
            }
        }

        int row = i - i % 3;
        int col = j - j % 3;

        for (int x = 0; x < 3; x++) {
            for (int y = 0; y < 3; y++) {
                if (board[x + row][y + col] == val) {
                    return false;
                }
            }
        }
        return true;
    }