Leetcode 36: Valid Sudoku

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.

The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

A partially filled sudoku which is valid.

 

Note:
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.

 

public class Solution {
    public bool IsValidSudoku(char[,] board) {
        int rows = board.GetLength(0), cols = board.GetLength(1);
        if (rows != 9 || cols != 9) return false;  
        
        var rused = new bool[9, 9];
        var cused = new bool[9, 9];
        var kused = new bool[9, 9];
        
        for (int i = 0; i < 9; i++)
        {
            for (int j = 0; j < 9; j++)
            {
                var c = board[i, j];
                if (c != '.')
                {
                    var index = (int)c - (int)'1';
                    var k = i / 3 * 3 + j / 3;
                    if (rused[i, index] || cused[j, index] || kused[k, index]) return false;
                    rused[i, index] = true;
                    cused[j, index] = true;
                    kused[k, index] = true;
                }
                        
            }
        }
        
        return true;
    }
}