Leetcode Valid Sudoku

class Solution {

private:

    // only used by _isValidSudoku

    int row[9];

    int col[9];

    int blk[9];

public:

    bool _isValidSudoku(vector<vector<char> >& board) {

        if (board.empty()) return true;

        memset(row, 0, sizeof(row));

        memset(col, 0, sizeof(col));

        memset(blk, 0, sizeof(blk));

        int rm, cm, bm;

        for (int i=0; i<9; i++) {

            int base = i / 3 * 3;

            for (int j=0; j<9; j++) {

                char ch = board[i][j];

                if (ch == '.') continue;

                int msk = 0x1<<(ch - '0');

                int blk_idx = base + j / 3;

                rm = msk|row[i];

                cm = msk|col[j];

                bm = msk|blk[blk_idx];

                if (rm == row[i] || cm == col[j] || bm == blk[blk_idx]) {

                    return false;

                }

                row[i] = rm;

                col[j] = cm;

                blk[blk_idx] = bm;

            }

        }

        return true;

    }

    

    bool isValidSudoku(vector<vector<char> >& board) {

        if (board.empty()) return true;

        int mx = board.size() - 1;

        int my = board[0].size() - 1;

        // each row

        for (int i=0; i <= my; i++) {

            if (!isValidRegion(board, 0, i, mx, 0)) return false;

        }

        // each column

        for (int i=0; i <= mx; i++) {

            if (!isValidRegion(board, i, 0, 0, my)) return false;

        }

        // each block

        for (int i=0; i<3; i++) {

            for (int j=0; j<3; j++){

                if (!isValidRegion(board, j*3, i*3, 2, 2)) return false;   

            }

        }

        return true;

    }

    bool isValidRegion(vector<vector<char> >& board, int sx, int sy, int dx, int dy) {

        char count[10];

        for (int i=0; i<10; i++) count[i] = 0;

        

        for (int i=sy + dy; i >= sy; i--) {

            for (int j=sx + dx; j >= sx; j--) {

                char num = board[i][j];

                if (num == '.') continue;

                if (num > '9' || num < '0') return false;

                if (++count[num-'0'] > 1) return false;

            }    

        }

        return true;

    }

};