36. 有效的数独 #

原题链接：LeetCode 36. 有效的数独

题目描述 #

请你判断一个 9 x 9 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。

- 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）

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。

- 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：**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 解释：除了第一行的第一个数字从 5 改为 **8 **以外，空格内其他数字均与 示例1 相同。 但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。

提示：

- `board.length == 9`

- `board[i].length == 9`

- `board[i][j]` 是一位数字（`1-9`）或者 `'.'`

难度： Medium

题解代码 #

/**
 * @param {character[][]} board
 * @return {boolean}
 */
 var isValidSudoku = function(board) {
  for (let i = 0; i < 9; i++) {
    for (let j = 0; j < 9; j++) {
      if (board[i][j] === '.') continue
      // 替换当前值
      const temp = board[i][j]
      board[i][j] = '.'
      if (!isValid(board, i, j, temp)) return false
      board[i][j] = temp
    }
  }
  return true
};

function isValid (board, row, col, k) {
  const x = Math.floor(row / 3) * 3
  const y = Math.floor(col / 3) * 3
  // 9x9
  for (let i = 0; i < 9; i++) {
    if (board[row][i] === k || board[i][col] === k) return false
  }
  // 3x3
  for (let i = 0; i < 3; i++) {
    for (let j = 0; j < 3; j++) {
      if (board[x + i][y + j] === k) return false
    }
  }
  return true
}