IT僧

Input: 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"]]
Output: true

Input: 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"]]
Output: false
Explanation: Same as Example 1, except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit 1-9 or '.'.

var isValidSudoku = function(board) {
    
    for(let i = 0; i < 9; i++) {
        // each line
        const chcekRow = new Set()
        for(let j = 0; j < 9; j++ ) {
            if (board[i][j] === '.') continue
            if (!chcekRow.has(board[i][j])) {
                chcekRow.add(board[i][j])
            } else {
                return false
            }
        }
        // each col
        const checkCol = new Set()
        for(let k = 0; k < 9; k++ ) {
            if(board[k][i] === '.') continue
            if (!checkCol.has(board[k][i])) {
                checkCol.add(board[k][i])
            } else {
                return false
            }
        }
        // each 3 x 3
        const groupCol = i % 3
        const groupRow = Math.floor(i/3)
        const checkBox = new Set()
        for(let l = groupCol * 3; l < groupCol * 3 + 3; l++ ) {
            for(let m = groupRow * 3; m < groupRow * 3 + 3; m++) {
                if(board[l][m] === '.') continue
                if (!checkBox.has(board[l][m])) {
                    checkBox.add(board[l][m])
                } else {
                    return false
                }
            }
        }
    }
    return true
};

思路

將驗證分成三個部分， 行, 列, 格

行, 列 驗證比較簡單，不贅述。

每隔的部分就需要稍微多想一下，因為是 9 x 9 的題目，所以拆解後會變成 9 個 3×3 的格子。
所以第一個大 loop 是 9個大格子，第二個 loop 是每格的 x 軸，第三個 loop 是每格的 y 軸。
這邊必須計算起始格的偏移量。
假設現在是第 i 個 3 x 3 格，每三格要換行，所以每個裡面起始的 x 位置會是 i / 3 * 3 ， y 的位置則是 Math.floor( i / 3) * 3
計算出來每一個 3×3 格相對大格的位置是 [0][0], [3][0], [6][0], [0][3], [3][3], [6][3], [0][6], [3][6], [6][6]
得到每格位置後，再偏移 3 * 3 去計算內容是否重複