36. 有效的数独

题目链接：https://leetcode-cn.com/problems/valid-sudoku/

思路：用三个数组分别标记一下。signRow[行][值]、signCol[列][值]、signCell[小正方形][值]，标记 (1 - 9) 是不是被用过即可（代码里面标记的 0 - 8 ，一个意思的，只是为了节约一丢丢空间而已）。

上代码：

class Solution {

    private val signRow = Array(9) { BooleanArray(9) }
    private val signCol = Array(9) { BooleanArray(9) }
    private val signCell = Array(3) { Array(3) { BooleanArray(9) } }

    fun isValidSudoku(board: Array<CharArray>): Boolean {
        for (i in 0 until 9) {
            for (j in 0 until 9) {
                if (board[i][j] != '.') {
                    val value = board[i][j] - '0' - 1
                    if (signRow[i][value] || signCol[j][value] || signCell[i / 3][j / 3][value]) {
                        return false
                    }
                    signRow[i][value] = true
                    signCol[j][value] = true
                    signCell[i / 3][j / 3][value] = true
                }
            }
        }
        return true
    }
}