class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board)
    {
        uint8_t i = 0, j = 0, k = 0, l = 0, x = 0, y = 0;
        vector<char> blk;
        //todo: check sizes of vectors

        //rows
        for(i = 0; i < 9; ++i)
        {
            if(!isValidBlk(board[i]))
            {
                return false;
            }
        }

        //cols
        for(i = 0; i < 9; ++i)
        {
            blk.clear();
            for(j = 0; j < 9; ++j)
            {
                blk.push_back(board[i][j]);
            }

            if(!isValidBlk(blk))
            {
                return false;
            }
        }

        //boxes
        // i,j
        // 0,0 1,0 2,0
        // 0,1 1,1 2,1
        // 0,2 1,2 2,2
        for(i = 0; i < 3; ++i)
        {
            blk.clear();
            y = 3 * i;
            for(j = 0; j < 3; ++j)
            {
                x = 3 * j;
                for(k = 0; k < 3; ++k)
                {
                    for(l = 0; l < 3; ++l)
                    {
                        blk.push_back(board[x+k][y+l]);
                    }
                }
            }

            if(!isValidBlk(blk))
            {
                return false;
            }
        }

        return true;
    }
private:
    bool isValidBlk(vector<char>& blk)
    {
        char values[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
        uint8_t index = 0, i;

        for(i = 0; i < 9; ++i)
        {
            index = isValidNum(blk[i]) ? (blk[i] - '0') : 0;
            if(index && //only check if not '.' (short circuit)
               values[index] == 0)
            {
                return false;
            }
            values[index] = 0;
        }
        return true;
    }

    bool isValidNum(uint8_t input) {
        if (input >= '1' && input <= '9')
        {
            return true;
        }
        return false;
    }
};