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✍️Younglina🕐2022-07-15 🔗 dfs中等

题目描述

15. 三数之和
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 '.'

思路

分三部分判断，行、列、块中是否存在重复的数字，初始化三个哈希表，以行号-数字、列号-数字、块号-数字的方式记录出现的数字。
难度在于块的计算方式详细解答

题解

javascript
var isValidSudoku = function(board) {
    let [rows, cols, blocks] = [{},{},{}]
    for(let i=0;i<9;i++){
        for(let j=0;j<9;j++){
            let num = board[i][j]
            if(num!=='.'){
                let blockIdx = parseInt(i/3)*3 + parseInt(j/3)
                if(rows[`${i}-${num}`] || cols[`${j}-${num}`] ||blocks[`${blockIdx}-${num}`]){
                    return false
                }
                rows[`${i}-${num}`]  = true
                cols[`${j}-${num}`]  = true
                blocks[`${blockIdx}-${num}`]  = true
            }
        }
    }
    return true
};