36. 有效的数独

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 '.'

 

/**
 * @param {character[][]} board
 * @return {boolean}
 */
var isValidSudoku = function(board) {
 //数独的每一行中每个数字的出现次数
 const rows = new Array(9).fill(0).map(()=>new Array(9).fill(0));
 //数独的每一列中每个数字的出现次数
 const columns = new Array(9).fill(0).map(()=>new Array(9).fill(0));
 //数独的每一个九宫格中的每个数字的出现次数
 const subboxes=new Array(3).fill(0).map(()=>new Array(3).fill(0).map(()=>new Array(9).fill(0)));
 for(let i =0;i<9;i++){
     for(let j =0;j<9;j++){
         const c = board[i][j];
         if(c!=='.'){
             const index = c.charCodeAt()-'0'.charCodeAt()-1;
             rows[i][index]++;
             columns[j][index]++;
             subboxes[Math.floor(i/3)][Math.floor(j/3)][index]++;
             if(rows[i][index]>1||columns[j][index]>1||subboxes[Math.floor(i/3)][Math.floor(j/3)][index]>1){
                 return false;
             }
         }
     }
 }
 return true;
};