请你判断一个 9x9 的数独是否有效。只需要 根据以下规则 ，验证已经填入的数字是否有效即可。

    1. 数字 1-9 在每一行只能出现一次。
    2. 数字 1-9 在每一列只能出现一次。
    3. 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。
    注意：

    • 一个有效的数独（部分已被填充）不一定是可解的。
    • 只需要根据以上规则，验证已经填入的数字是否有效即可。

    示例 1：
    image.png

    1. 输入：board = 
    2. [["5","3",".",".","7",".",".",".","."]
    3. ,["6",".",".","1","9","5",".",".","."]
    4. ,[".","9","8",".",".",".",".","6","."]
    5. ,["8",".",".",".","6",".",".",".","3"]
    6. ,["4",".",".","8",".","3",".",".","1"]
    7. ,["7",".",".",".","2",".",".",".","6"]
    8. ,[".","6",".",".",".",".","2","8","."]
    9. ,[".",".",".","4","1","9",".",".","5"]
    10. ,[".",".",".",".","8",".",".","7","9"]]
    11. 输出：true

    示例 2：

    输入：board = 
[["8","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：false

    提示：

    • board.length == 9
    • board[i].length == 9

    • board[i][j] 是一位数字或者 ‘.’

      /**
* @param {character[][]} board
* @return {boolean}
*/
var isValidSudoku = function(board) {
  // 步骤 1：初始化横、纵以及小九宫格
  const rows = [],
      columns = [],
      boxes = [];
  for (let i = 0; i < 9; i++) {
      rows[i] = [];
      columns[i] = [];
      boxes[i] = [];
  }
  // 对应的 rows 为 [[], [], [], [], [], [], [], [], []]

  // 步骤 2：遍历填充值
  for (let i = 0; i < 9; i++) {
      for (let j = 0; j < 9; j++) {

          // 获取值
          const value = board[i][j];

          // 先判断非 . 元素
          if (value !== '.') {

              // 检验横排
              if (!rows[i].includes(value)) {
                  rows[i].push(value);
              } else {
                  return false;
              }

              // 检验竖排
              if (!columns[j].includes(value)) {
                  columns[j].push(value);
              } else {
                  return false;
              }

              // 检查盒子
              const boxIndex = Math.floor(i / 3) * 3 + Math.floor(j / 3); // 对应的盒子
              if (!boxes[boxIndex].includes(value)) {
                  boxes[boxIndex].push(value);
              } else {
                  return false;
              }
          }
      }
  }

  // 步骤 3：如果没有问题，就是真的，返回 true
  return true;
};