Valid Sudoku

Problem statement

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.

Example 1:

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

Example 2:

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: falseExplanation: 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 '.'.

My solution

/**
 * @param {character[][]} board
 * @return {boolean}
 */
var isValidSudoku = function(board) {
    const memo = new Set();
    for (let i = 0; i < board.length; i++) {
        for (let j = 0; j < board[0].length; j++) {
            const value = board[i][j];
            
            if (value === ".") {
                continue;
            }
            
            const boxNum = 3 * Math.floor(i/3) + Math.floor(j/3)
            
            let inRow = `row: ${i}, value: ${value}`;
            let inCol = `col: ${j}, value: ${value}`;
            let inSubBox = `subBox: ${boxNum}, value: ${value}`;
            
            if (memo.has(inRow) || memo.has(inCol) || memo.has(inSubBox)) {
                return false;
            }
            
            memo.add(inRow)
            memo.add(inCol)
            memo.add(inSubBox)
            
        }
    }
    
    return true;
};