36. Valid Sudoku

Problem

Tags: Array, Hash Table, Matrix

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: 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 '.'.

Code

JS

// 36. Valid Sudoku (6/29/53723)
// Runtime: 121 ms (30.78%) Memory: 40.96 MB (94.91%) 

/**
 * @param {character[][]} board
 * @return {boolean}
 */
function isValidSudoku(board) {
    function validateBox(X, Y) {
        let s = new Set(), c = 0;
        for(let i = 0; i < 3; i++)
            for(let j = 0; j < 3; j++) 
                if(board[X*3 + i][Y*3 + j] !== ".") {
                    c++;
                    s.add(board[X*3 + i][Y*3 + j]);
                }
        return s.size === c;
    }
    function validateRow(n) {
        let s = new Set(), c = 0;
        for(let i = 0; i < 9; i++)
            if(board[n][i] !== ".") {
                c++;
                s.add(board[n][i]);
            }
        return s.size === c;
    }
    function validateCol(n) {
        let s = new Set(), c = 0;
        for(let i = 0; i < 9; i++)
            if(board[i][n] !== ".") {
                c++;
                s.add(board[i][n]);
            }
        return s.size === c;
    }
    for(let i = 0; i < 3; i++)
        for(let j = 0; j < 3; j++)
            if(!validateBox(i, j)) return false;
    for(let i = 0; i < 9; i++) 
        if(!validateRow(i)) return false;
    for(let i = 0; i < 9; i++) 
        if(!validateCol(i)) return false;
    return true;
};