36. Valid Sudoku

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.

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        unordered_set<string> s;

        for(int row = 0; row < 9; row++) {
            for(int col = 0; col < 9; col++) {
                if(board[row][col] == '.') continue;
                string rowVal = "row" + to_string(row) + board[row][col];
                string colVal = "col" + to_string(col) + board[row][col];
                string cellVal = "cell" + to_string(row / 3 * 3 + col / 3) + board[row][col];
                if(s.count(rowVal) || s.count(colVal) || s.count(cellVal)) {
                    return false;
                }
                s.insert(rowVal);
                s.insert(colVal);
                s.insert(cellVal);
            }
        }
        return true;
    }
};

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        bool rows[9][9] {false, }, cols[9][9] {false, }, cells[9][9] {false, };
        
        for(int row = 0; row < 9; row++) {
            for(int col = 0; col < 9; col++) {
                if(board[row][col] == '.') continue;
                if(rows[row][(board[row][col] & 0b1111) - 1] || cols[col][(board[row][col] & 0b1111) - 1] || cells[row / 3 * 3 + col / 3][(board[row][col] & 0b1111) - 1] )
                    return false;
                rows[row][(board[row][col] & 0b1111) - 1] = cols[col][(board[row][col] & 0b1111) - 1] = cells[row / 3 * 3 + col / 3][(board[row][col] & 0b1111) - 1] = true;
            }
        }
        return true;
    }
};