判断一个 9×9 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 3×3 宫内只能出现一次。
上图是一个部分填充的有效的数独。
数独部分空格内已填入了数字，空白格用 ‘.’ 表示。
示例 1: 输入:
[
[“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:
[
[“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 ` 3×3` 宫内有两个 `8` 存在, 因此这个数独是无效的。
说明: 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。给定数独序列只包含数字 1-9 和字符 ‘.’。给定数独永远是 9×9 形式的。
答案参考：
/**
* @param {character[][]} board
* @return {boolean}
*/
var isValidSudoku = function(board) {
// 检查每一行
for (let arr of board) {
let row = []
for (let c of arr) {
if (c !== ‘.’) row.push(c);
}
let set = new Set(row)
if (set.size !== row.length) return false;
}
// 检查每一列
for (let i = 0; i < 9; i++) {
let col = []
board.map(arr => {
if (arr[i] !== ‘.’) col.push(arr[i])
})
let set = new Set(col)
if (set.size !== col.length) return false;
}
// 检查每个小方块
for (let x = 0; x < 9; x += 3) {
for (let y = 0; y < 9; y += 3) {
let box = []
for (let a = x; a < 3 + x; a ++) {
for (let b = y; b < 3 + y; b ++) {
if (board[a][b] !== ‘.’) box.push(board[a][b])
}
}
let set = new Set(box)
if (set.size !== box.length) return false
}
}
return true
};